Acute Kidney Injury ICD-10 Codes: N17.9 and the Full N17 Family Explained for FY 2027

Every acute kidney injury ICD-10 claim that goes out coded as N17.9 when the chart actually documents acute tubular necrosis is a coding error, and on an inpatient claim it can mean a lower DRG. Coders defaulting to N17.9 without checking whether the physician documented tubular, cortical, or medullary necrosis are leaving revenue on the table and creating audit exposure at the same time.

The FY 2027 ICD-10-CM code set, in effect from October 1, 2026, through September 30, 2027, kept the N17 series unchanged. What matters is the payment math: under MS-DRG v44, N17.0, N17.1, and N17.2 are major complications or comorbidities (MCCs), while N17.8 and N17.9 are complications or comorbidities (CCs). Practices that treat N17.9 as the default AKI code can land inpatient cases in a lower DRG than the documentation supports.

Two other changes shape this cycle. KDIGO posted a draft of its 2026 AKI/AKD guideline, the first major update to its AKI guideline since 2012, and closed public review on May 11, 2026. ACDIS and AHIMA released a 2026 update to their compliant query guidelines on August 20, 2026. If you’re a biller, CDI specialist, or nephrology practice manager, here’s what the FY 2027 ICD-10-CM cycle asks of you.

This guide covers the full acute kidney injury ICD-10 code family, FY 2027 documentation requirements for each sub-code, KDIGO clinical staging versus N17 sub-code relationships, AKI-on-CKD sequencing, sepsis-AKI sequencing per Section I.C.1.d, DRG impact, comorbid coding scenarios, CDI query templates, and a compliance checklist you can use at the point of chart review.

Quick Answer

The ICD-10-CM code for acute kidney injury (AKI) is N17.9 (Acute kidney failure, unspecified) when the cause and pattern are not documented. The complete N17 series for FY 2027 contains five billable codes: N17.0 (with tubular necrosis), N17.1 (with acute cortical necrosis), N17.2 (with medullary necrosis), N17.8 (other acute kidney failure), and N17.9 (unspecified). Codes N17.3 through N17.7 do not exist in ICD-10-CM. AKI superimposed on chronic kidney disease requires both N17.x and N18.x.

What Is Acute Kidney Injury (AKI)?

Acute kidney injury is a rapid decline in kidney function that develops over hours or days. It’s not a single disease. It’s a syndrome with multiple causes, multiple patterns, and multiple severity levels. Understanding the clinical framework is what separates coders who get AKI right from coders who default to N17.9 on every chart.

The acute kidney injury ICD-10 coding system captures this syndrome through the N17 category, which organizes the condition by anatomical and pathological pattern. Before the N17 codes make sense, the clinical picture needs to be clear.

AKI vs Acute Renal Failure (ARF): Same Condition, Different Terminology

Acute kidney injury and acute renal failure are clinically synonymous in modern nephrology. Both describe the same rapid deterioration of kidney function. Both code to the N17 category in ICD-10-CM. AKI became the preferred term after the AKIN criteria of 2007 and the KDIGO 2012 Clinical Practice Guideline.

Older physician charts will still use ARF. That’s fine for coding purposes. Both terms map to N17.x without distinction.

KDIGO Diagnostic Criteria for AKI

Acute kidney injury is diagnosed per KDIGO 2012 criteria when one of the following is met: serum creatinine increase of 0.3 mg/dL or more within 48 hours, serum creatinine increase to 1.5 times baseline within 7 days, or urine output less than 0.5 mL/kg per hour for 6 hours.

Coding teams reviewing acute kidney injury ICD-10 documentation should watch for the final KDIGO 2026 AKI/AKD guideline, which KDIGO is still preparing after public review. Until it’s published, the KDIGO 2012 Clinical Practice Guideline for Acute Kidney Injury remains the active clinical reference. Code assignment still follows the provider’s documented diagnosis, not the clinical criteria behind it (FY 2027 Official Guidelines, Section I.A.19).

Prerenal vs Intrinsic vs Postrenal AKI

Clinically, AKI falls into three categories based on the location and mechanism of injury. Prerenal AKI results from reduced blood flow to the kidneys (dehydration, septic shock, heart failure). Intrinsic AKI results from direct kidney damage (tubular necrosis, cortical necrosis, glomerulonephritis). Postrenal AKI results from obstruction to urine outflow.

This classification matters for coding because it drives which N17 sub-code applies. Intrinsic AKI, particularly tubular injury, is the scenario where physicians most often document the pattern specificity that supports N17.0, N17.1, or N17.2.

The N17 Code Family: All Five Acute Kidney Injury ICD-10 Codes for FY 2027

The N17 category in ICD-10-CM contains all codes for acute kidney injury, also documented as acute kidney failure or acute renal failure. The category itself (N17) is not a billable code. Claims must report a specific subcategory: N17.0, N17.1, N17.2, N17.8, or N17.9. The FY 2027 edition of these codes took effect October 1, 2026, and remains in force through September 30, 2027.

The acute kidney injury ICD-10 code landscape is simpler than many coders assume. There are exactly five billable options. Knowing which one applies is a documentation question, not a coding complexity question.

ICD-10-CM Code	Full Description	Common Causes	Billable?	DRG Impact
N17	Acute kidney failure (category header)	None	No	Not assignable
N17.0	Acute kidney failure with tubular necrosis	Ischemia, sepsis, nephrotoxic agents, contrast media	Yes	MCC
N17.1	Acute kidney failure with acute cortical necrosis	Severe sepsis, obstetric complications, major trauma	Yes	MCC
N17.2	Acute kidney failure with medullary necrosis	Sickle cell disease, severe dehydration, analgesic abuse	Yes	MCC
N17.8	Other acute kidney failure	Causes not classified elsewhere	Yes	CC
N17.9	Acute kidney failure, unspecified	Cause not documented	Yes	CC

Reference the FY 2027 ICD-10-CM code files from CMS for the complete tabular listing.

N17.0: Acute Kidney Failure With Tubular Necrosis

N17.0 is the most common form of intrinsic AKI and the code most frequently missed when coders default to N17.9. Acute tubular necrosis (ATN) results from ischemia or nephrotoxic exposure. Documentation must explicitly state “ATN,” “acute tubular necrosis,” or “renal tubular necrosis.” If the note only says “ischemic tubular damage” or “nephrotoxic tubular injury,” query to confirm ATN.

Elevated creatinine alone doesn’t get you here. The physician’s diagnostic language does. This code pairs frequently with sepsis and contrast media scenarios and is an MCC under MS-DRG v44 when reported as a secondary diagnosis, unless the principal diagnosis excludes it.

N17.1: Acute Kidney Failure With Acute Cortical Necrosis

N17.1 is rare and often irreversible. It’s most common in severe obstetric complications: placental abruption, eclampsia, and septic abortion. Major trauma and severe sepsis are additional triggers. Documentation must explicitly state “acute cortical necrosis” or “cortical necrosis.”

Because of its association with catastrophic obstetric events, this code sometimes appears paired with pregnancy-related complications codes. Query the physician when AKI occurs in the obstetric context and the documentation is vague.

N17.2: Acute Kidney Failure With Medullary Necrosis

N17.2 is less common than N17.0 but appears in specific clinical scenarios: sickle cell disease, severe analgesic abuse (especially NSAID overuse), and severe dehydration. Documentation must explicitly state “medullary necrosis” or “papillary necrosis.” The physician’s diagnostic language drives this assignment; presuming medullary necrosis from lab values alone isn’t acceptable.

N17.8: Other Acute Kidney Failure

N17.8 captures another specified type of acute kidney failure that doesn’t fit N17.0 through N17.2. Check the ICD-10-CM Index before you use it, because many documented causes route elsewhere. Postoperative kidney failure documented as a complication goes to N99.0 with an additional N17 code for the type, and acute tubulo-interstitial nephritis is classified to N10. N17.8 is a CC, not an MCC.

N17.9: Acute Kidney Failure, Unspecified

N17.9 is the code to use when AKI or ARF is documented but the underlying cause and pathological pattern aren’t specified. It includes “acute kidney injury (nontraumatic).” Two exclusion notes apply. The N17 category has an Excludes1 note for posttraumatic renal failure (T79.5-, which needs a 7th character), so you don’t code it with N17.x. N17.9 has an Excludes2 note for traumatic kidney injury (S37.0-), which you can code alongside it when both are present. This is the code billers should query against, not default to.

Coding Alert: Codes N17.3, N17.4, N17.5, N17.6, and N17.7 Do Not Exist

Some online coding references incorrectly list N17.3 as “AKI Stage 3” or imply that KDIGO Stage 1, 2, and 3 map to N17.1, N17.2, and N17.3. This is factually wrong. The N17 series in ICD-10-CM contains only five billable codes: N17.0, N17.1, N17.2, N17.8, and N17.9. KDIGO clinical staging does not map directly to N17 sub-codes. The KDIGO staging section below explains the correct relationship.

FY 2027 ICD-10-CM Updates and Why They Matter for AKI Coding

The acute kidney injury ICD-10 code set didn’t change in FY 2027: N17, N18, N19, and N14 all carry over as is. What you need to apply is the payment and documentation context around them, from the CC and MCC split under MS-DRG v44 to the 2026 query guidelines. Here’s what the current cycle asks for.

FY 2027 ICD-10-CM Effective Dates and the AKI Code Set

FY 2027 ICD-10-CM took effect October 1, 2026, and runs through September 30, 2027. The N17 series is unchanged from FY 2026, with no new sub-codes and no descriptor changes. One new related code, Z77.013 (contact with and suspected exposure to gadolinium), matters for the contrast discussion later in this guide. Per the FY 2027 ICD-10-CM Official Guidelines for Coding and Reporting, code assignment is based on the provider’s diagnostic statement, so N17.x requires explicit documentation of acute kidney injury, acute renal failure, or acute kidney failure.

Lab abnormalities without physician diagnostic language don’t support N17.x assignment. That rule has always existed, and auditors check for it.

Official Guidelines Sections That Govern AKI Coding

Four sections of the FY 2027 ICD-10-CM Official Guidelines directly affect AKI coding. Section I.C.1.d governs sepsis sequencing and determines whether sepsis or AKI drives principal diagnosis selection when both are present (covered in the sepsis section below). Section I.C.14 covers the genitourinary chapter, but its only guideline is for chronic kidney disease, so AKI follows the general rules and the Tabular notes at N17.

Section II covers the selection of principal diagnosis for inpatient encounters and is relevant for AKI-on-CKD cases where acute and chronic conditions are both present. Section III governs reporting of additional diagnoses, which applies when AKI is a secondary condition in a sepsis-primary or surgery-primary encounter.

FY 2027 Status and What Comes Next

CMS released the FY 2027 ICD-10-CM files in the summer of 2026, and they took effect October 1, 2026. The KDIGO 2026 AKI/AKD Guideline (public review draft, March 2026) closed public review on May 11, 2026, and KDIGO hasn’t published the final version yet. When it does, expect changes to clinical definitions and CDI query triggers, not to ICD-10-CM codes, because code assignment follows the provider’s diagnosis.

The N17 category carries an Excludes1 note for posttraumatic renal failure (T79.5-), and N17.9 carries an Excludes2 note for traumatic kidney injury (S37.0-).

Need help keeping your AKI documentation aligned with FY 2027 rules? One O Seven RCM’s certified coders review nephrology documentation and catch the specificity gaps that drive AKI denials. Our medical billing services team handles the entire workflow from documentation review to claim submission.

KDIGO Clinical Staging vs N17 Sub-Codes: The Critical Difference Most Coders Miss

Some acute kidney injury ICD-10 coding pages imply, or state outright, that KDIGO Stage 1 maps to N17.1, Stage 2 maps to N17.2, and Stage 3 maps to N17.3. Every part of that statement is wrong. N17.3 doesn’t exist. And the staging-to-subcode mapping doesn’t exist either. Here’s the actual relationship.

KDIGO clinical staging classifies AKI by clinical severity using serum creatinine and urine output thresholds. N17 sub-codes in ICD-10-CM classify AKI by anatomical and pathological pattern (tubular, cortical, or medullary necrosis). These two systems are complementary, not equivalent.

What KDIGO Clinical Staging Measures

KDIGO staging uses lab values and urine output to define three severity levels. Stage 1, 2, and 3 reflect increasing clinical severity and inform clinical management decisions, not ICD-10-CM code selection.

KDIGO Stage	Serum Creatinine Criteria	Urine Output Criteria
Stage 1	1.5 to 1.9 times baseline OR ≥0.3 mg/dL increase	<0.5 mL/kg/h for 6 to 12 hours
Stage 2	2.0 to 2.9 times baseline	<0.5 mL/kg/h for ≥12 hours
Stage 3	3.0 times baseline OR increase to ≥4.0 mg/dL OR initiation of RRT OR, in patients under 18, eGFR below 35 mL/min per 1.73 m²	<0.3 mL/kg/h for ≥24 hours OR anuria for ≥12 hours

These thresholds come from the KDIGO 2012 guideline, which remains the published standard. KDIGO’s 2026 draft, which finished public review in May 2026, adds structural biomarkers to the AKI definition, so check the final version when it’s published.

What N17 Sub-Codes Describe

N17.0 through N17.9 describe anatomical and pathological findings, not clinical severity. Tubular necrosis, cortical necrosis, and medullary necrosis are histopathological patterns. They tell you what the kidney damage looks like at the tissue level. The “Other” code (N17.8) and “Unspecified” code (N17.9) handle everything that doesn’t fit the three named patterns.

Severity is one dimension. Pathological pattern is a different dimension. Both can and should be documented, but they’re not the same thing.

Why KDIGO Stage and N17 Sub-Code Are Not Interchangeable

KDIGO Stage 1 does not equal N17.1. N17.2 does not equal KDIGO Stage 2. The numeric overlap between the two systems is coincidental, not equivalent.

Here’s the real-world example. A patient with KDIGO Stage 2 AKI from sepsis-induced acute tubular necrosis codes to N17.0, not N17.2. The KDIGO Stage 2 designation reflects serum creatinine 2.0 to 2.9 times baseline. The N17.0 designation reflects the documented pathological pattern (tubular necrosis). Neither number has anything to do with the other.

For CDI: query the physician for both dimensions when possible. Document the KDIGO stage for clinical context and the pathological pattern for coding specificity. They’re complementary data points, not competing ones.

AKI Documentation Requirements: What Providers Must Include for Each N17 Code

This section gives code-specific requirements that translate directly to correct N17.x assignment. These are the standards billers and CDI specialists need to apply at the point of chart review.

The acute kidney injury ICD-10 code assignment stands or falls on physician language. Lab values support the diagnosis; they don’t establish it. Here’s what each code needs.

Universal Documentation Requirements for AKI

Any N17.x code assignment requires six documentation elements. Explicit acuity language: “acute kidney injury,” “acute renal failure,” or “acute kidney failure.” Phrases like “new-onset kidney dysfunction” or “sudden rise in creatinine” don’t support N17 on their own, so query. Lab support: serum creatinine trend with dates and values, BUN, eGFR trajectory, and urine output data.

The underlying cause must be documented when known (sepsis, dehydration, nephrotoxic agent, contrast media). The KDIGO stage should be documented if determinable from available clinical data. The POA indicator must be supportable from the admission documentation. Any treatment actions (IV fluids, nephrology consult, dialysis initiation) strengthen the medical necessity record.

Documentation Requirements Per N17 Code

Each specific sub-code has its own documentation threshold:

• N17.0: Must state “ATN,” “acute tubular necrosis,” or “renal tubular necrosis” (query if the note only says “ischemic” or “nephrotoxic” tubular injury)
• N17.1: Must state “acute cortical necrosis” or “cortical necrosis” (often with obstetric or major trauma context)
• N17.2: Must state “medullary necrosis” or “papillary necrosis” (often with sickle cell or analgesic context)
• N17.8: Must state another specified type of acute kidney failure that doesn’t fit N17.0 through N17.2 (check the Index first: postoperative kidney failure goes to N99.0 plus N17, and acute tubulo-interstitial nephritis goes to N10)
• N17.9: AKI or ARF is documented but the cause and pattern are not specified

To support N17.0 (acute tubular necrosis), physician documentation must explicitly state acute tubular necrosis, ATN, or renal tubular necrosis. Lab abnormalities alone (elevated serum creatinine, elevated BUN) without diagnostic language are insufficient for N17.0 assignment.

AKI assignment requires explicit diagnostic language: acute kidney injury, acute renal failure, or acute kidney failure. Without it, the chart may support only N18.x (chronic kidney disease), N19 (unspecified kidney failure), or N28.9 for “renal insufficiency,” and an abnormal creatinine alone is a finding (R94.4), not a diagnosis.

AKI Documentation Template

The following structured template, built by our coding team, supports complete AKI documentation at the point of care:

AKI Documentation Template:

• AKI Stage [1 / 2 / 3] per KDIGO criteria
• Baseline Cr: ___ mg/dL (Date: ___)
• Current Cr: ___ mg/dL (increased ___%)
• Urine output: ___ mL/hr (___ mL/24h)
• Etiology: [ ] Prerenal [ ] Intrinsic [ ] Postrenal
• Pattern: [ ] Tubular [ ] Cortical [ ] Medullary [ ] Other [ ] Unspecified

This template supports accurate acute kidney injury ICD-10 code selection by capturing both the KDIGO stage (clinical severity) and the pattern (N17 sub-code driver) in a single provider-facing entry.

AKI vs CKD vs Acute-on-Chronic: Disambiguating the N17 and N18 Boundary

Three high-volume acute kidney injury ICD-10 coding scenarios cluster around the AKI and CKD boundary: pure AKI in a patient without CKD, pure CKD without acute decompensation, and AKI superimposed on existing CKD. Getting the sequencing and code combination right is critical for accurate DRG assignment and denial avoidance.

AKI (N17.x) vs CKD (N18.x): The Acuity Distinction

AKI (N17.x) reflects rapid loss of kidney function over hours or days, often reversible with treatment. CKD (N18.x) reflects sustained loss of kidney function over three or more months. The two are coded together (acute-on-chronic) when both are clinically documented.

The distinction matters because acuity language drives N17.x assignment. “Chronic” language (reduced GFR for more than three months, long-standing proteinuria) drives N18.x. Mixing them up generates incorrect principal diagnosis selection and DRG misassignment.

Acute-on-Chronic Kidney Disease: When Both Apply

When AKI develops in a patient with existing CKD, both conditions must be coded. Use the appropriate N17.x code plus the appropriate N18.x stage code. Sequencing: when the encounter is primarily for the acute event, N17.x is sequenced first. When the encounter is for CKD management and the AKI is incidental or resolving, CKD sequencing may lead.

Example: AKI on CKD Stage 3b = N17.9 + N18.32. Both codes are required; submitting only N17.9 undercodes the severity. The N18 codes also carry a “code first” note for hypertensive CKD (I12.-, I13.-) and diabetic CKD (E08.22 to E13.22), so report those when documented: for example, N17.9 + I12.9 + N18.32, sequenced by the reason for the admission.

When acute kidney injury is superimposed on chronic kidney disease, both N17.x and the appropriate N18.x stage code must be reported. The acute condition (N17.x) is sequenced first when it is the reason for the encounter.

AKI on CKD Reference Table

CKD Stage	CKD ICD-10 Code	Combined AKI on CKD Coding
CKD Stage 1	N18.1	N17.x + N18.1
CKD Stage 2	N18.2	N17.x + N18.2
CKD Stage 3, unspecified	N18.30	N17.x + N18.30
CKD Stage 3a	N18.31	N17.x + N18.31
CKD Stage 3b	N18.32	N17.x + N18.32
CKD Stage 4	N18.4	N17.x + N18.4
CKD Stage 5	N18.5	N17.x + N18.5
ESRD	N18.6	N17.x + N18.6
CKD Unspecified	N18.9	N17.x + N18.9

Both codes in the table are required; neither is optional when both conditions are documented. Per the KDIGO 2024 Clinical Practice Guideline for Evaluation and Management of CKD, CKD stage must be based on sustained abnormalities lasting at least three months, not transient lab changes.

Sepsis-Induced AKI: Sequencing Rules Per ICD-10-CM Section I.C.1.d

The sepsis-AKI scenario is the most common acute kidney injury ICD-10 coding challenge in the ICU, and it’s the one most frequently missequenced. The Official Guidelines are explicit on this point: when severe sepsis is present on admission, the systemic infection is the principal diagnosis, not N17.x. Here’s the correct rule.

The Sepsis Sequencing Rule

Per ICD-10-CM Official Guidelines Section I.C.1.d, when severe sepsis with AKI is present on admission and meets the definition of principal diagnosis, the systemic infection code is principal and N17.x is secondary, even when AKI is the immediate clinical concern. If severe sepsis develops after admission, the infection code and R65.2- are secondary, and the condition that led to the admission, which can be N17.x, stays principal. The AKI must also be linked to the sepsis to assign R65.2-; if the provider doesn’t make that link, query.

R65.20 vs R65.21: Two Different Sepsis Codes

R65.20 is severe sepsis without septic shock. It applies when sepsis with associated acute organ dysfunction, such as AKI, is documented without shock. R65.21 is severe sepsis with septic shock. The systemic infection code comes from the organism: A41.9 for unspecified sepsis or A41.51 for E. coli sepsis. A localized infection such as pneumonia (J18.9) is a separate, secondary code.

Sequencing for sepsis with AKI: underlying infection code FIRST, then R65.20 or R65.21, then N17.x. R65.20 and R65.21 are not used alone. They must be paired with the underlying infection code (A41.9 for unspecified sepsis, A41.51 for E. coli sepsis, or other specific infection code) and the organ dysfunction code (N17.x for AKI).

Sepsis-AKI Coding Examples

When AKI is documented as caused by sepsis, the sepsis code (R65.20 severe sepsis without septic shock or R65.21 severe sepsis with septic shock) is sequenced after the underlying infection code, with the appropriate N17.x code reported as a secondary diagnosis per ICD-10-CM Official Guidelines Section I.C.1.d.

Three common scenarios with their correct code strings:

Example 1: E. coli sepsis with severe sepsis and AKI with acute tubular necrosis Code string: A41.51 + R65.20 + N17.0

Example 2: Septic shock from pneumonia with unspecified AKI Code string: A41.9 + R65.21 + J18.9 + N17.9

Example 3: UTI-induced sepsis with AKI (see our ICD-10 code for UTI (N39.0) guide for the upstream coding) Code string: A41.51 + R65.20 + N39.0 + N17.9 (when E. coli is the documented organism)

Each example assumes severe sepsis was present on admission and follows Section I.C.1.d of the FY 2027 guidelines: systemic infection first, R65.2- next, then the localized infection and the organ dysfunction.

AKI as CC or MCC: DRG Impact for Hospital Inpatient Reimbursement

Most billers coding acute kidney injury ICD-10 claims know the N17.x codes. Fewer know that the five codes split into two payment tiers: three MCCs and two CCs. This section is for CDI specialists and revenue cycle leaders who need the DRG impact framed in operational terms.

What CC and MCC Mean for N17.x Codes

MCC stands for Major Complication or Comorbidity. CMS designates conditions as MCC, CC, or non-CC based on the resource intensity required to manage them. Under MS-DRG v44 (FY 2027), N17.0, N17.1, and N17.2 are MCCs, and N17.8 and N17.9 are CCs, subject to the CC exclusion list for the principal diagnosis. When a secondary diagnosis carries MCC status, it can shift the DRG grouping to a higher-weighted group with substantially higher reimbursement.

That split is the strongest case for specificity. When the provider documents acute tubular necrosis, the secondary diagnosis moves from N17.9 (a CC) to N17.0 (an MCC), and the case can move to the MCC tier of its DRG family. Check the FY 2027 relative weights in the IPPS final rule for the dollar impact at your hospital’s base rate.

MS-DRG Groupings Affected by N17.x

N17.x appearing as a secondary diagnosis on procedure-driven encounters can shift DRG assignment significantly. Three DRG variants within the kidney and urinary tract procedures group illustrate the stakes:

• DRG 673: Other kidney and urinary tract procedures with MCC (highest weight)
• DRG 674: Other kidney and urinary tract procedures with CC
• DRG 675: Other kidney and urinary tract procedures without CC/MCC (lowest weight)

A case in DRG 675 moves to DRG 674 when N17.8 or N17.9 is captured as a secondary diagnosis, and to DRG 673 when N17.0, N17.1, or N17.2 is captured, provided the principal diagnosis doesn’t exclude it. When AKI is the principal diagnosis, the case groups to the medical renal failure DRGs: 682 (with MCC), 683 (with CC), and 684 (without CC/MCC). Accurate N17 capture is a core part of revenue cycle management for hospital inpatient billing. Hospitals also see CO-234 bundling denials when AKI-related procedures are billed incorrectly; our CO-234 bundling denial guide covers that resolution path.

POA Indicator Decision Tree for AKI

For inpatient claims, the Present on Admission (POA) indicator on N17.x affects reimbursement and quality reporting.

Four values apply. Y means AKI was present at the time of admission. N means it developed after admission. U means the documentation is insufficient to determine POA status, and W means the provider can’t clinically determine it. N17 isn’t on the CMS hospital-acquired condition list, so a POA of N doesn’t trigger the HAC payment penalty, but it does feed quality measures such as PSI 10 when postoperative AKI requires dialysis.

For CDI workflow: review the admission creatinine against the most recent prior creatinine available. If the lab trajectory shows AKI was present on arrival but the admitting note doesn’t mention it, query the provider before the case closes.

Comorbid AKI Coding Scenarios: Contrast-Induced, Drug-Induced, Rhabdomyolysis, Hepatorenal, and Dehydration

Acute kidney injury ICD-10 coding rarely involves a single isolated condition. The five scenarios below account for the most common comorbid AKI presentations in billing. Each requires a specific code pairing and specific documentation language. General guidance isn’t enough at the claim level. Here are the exact code combinations.

Contrast-Induced AKI

Contrast-induced acute kidney injury is reported with the N17 code the documentation supports (N17.0 if ATN is documented, otherwise N17.9), paired with T50.8X5A (adverse effect of diagnostic agents, initial encounter). When the physician documents “contrast-induced nephropathy,” add N14.11; its Excludes2 note lets you report it with N17. FY 2027 also added Z77.013 for contact with and suspected exposure to gadolinium.

Documentation requirement: the physician must link the AKI to contrast administration and document when the contrast was given. “Elevated creatinine after CT scan” without the diagnostic linkage isn’t sufficient. This scenario is common in radiology, cardiology cath lab, and CT imaging. Sequencing follows the reason for the encounter.

Drug-Induced AKI and Nephrotoxicity

Drug-induced AKI pairs the appropriate N17.x code with a T-code from the T36-T50 series identifying the offending agent. Common offenders: aminoglycosides, NSAIDs, vancomycin, tacrolimus, and cisplatin. Documentation requirement: physician must explicitly state “drug-induced” or “nephrotoxic” as the mechanism.

The 7th character matters. Use “A” for initial encounter, “D” for subsequent encounter, and “S” for sequela. If the AKI resulted from a wrong dose given in error, code it as a poisoning (T36 to T50 with a 5th or 6th character of 1) instead of an adverse effect. Y63.6 covers underdosing or nonadministration of a needed drug, not this case.

Rhabdomyolysis-Induced AKI

Rhabdomyolysis-induced AKI is reported as M62.82 (rhabdomyolysis) plus the N17 code the documentation supports, with elevated creatine kinase values supporting the diagnosis. Myoglobin from muscle breakdown often damages the renal tubules, but coders can’t assume ATN: use N17.0 only when the provider documents ATN, and N17.9 otherwise. Traumatic rhabdomyolysis is coded T79.6XXA instead of M62.82.

Common clinical triggers include trauma, prolonged immobility, severe exertion, statin toxicity, and crush injuries. Documentation requirement: elevated CK values plus a physician statement explicitly linking AKI to rhabdomyolysis.

Hepatorenal Syndrome

Hepatorenal syndrome pairs K76.7 (hepatorenal syndrome) with the appropriate N17.x code when AKI is also explicitly documented by the physician. HRS is a specific clinical syndrome of AKI occurring in the context of advanced liver disease, most commonly cirrhosis. K76.7 is itself an MCC under MS-DRG v44.

Documentation requirement: explicit physician statement of “hepatorenal syndrome,” not just liver disease with elevated creatinine. The diagnosis requires clinical judgment and a formal physician attestation. This code often pairs with cirrhosis codes from the K70.x or K74.x series.

AKI Caused by Dehydration

Dehydration-induced AKI pairs the appropriate N17.x code with E86.0 (dehydration) or E86.1 (hypovolemia). Documentation requirement: the physician must explicitly state dehydration or hypovolemia as the cause of the AKI. “Elevated creatinine with poor fluid intake” without the causal linkage isn’t sufficient for the code pairing.

Sequencing follows the principal diagnosis rules in Section II: the condition chiefly responsible for the admission goes first. This scenario is common in elderly patients, gastroenteritis presentations, and post-surgical dehydration.

History of AKI Coding: When to Use Z87.448

Once an acute kidney injury ICD-10 claim is no longer reflecting active disease, the N17.x code stops. A lot of coders keep reporting N17.9 on follow-up encounters out of habit or because the problem list still shows it. That’s incorrect. Once the kidney injury has resolved and active treatment has stopped, the appropriate code is a history code.

Z87.448 (Personal history of other diseases of urinary system) is the history code for resolved AKI. It’s used when AKI is no longer clinically active and the encounter isn’t for AKI management. The active N17.x code should not be reported once the AKI has resolved. History codes tell the payer that a prior condition is relevant to current management without implying the condition is still active.

Z87.448 is appropriate when the prior AKI affects current clinical decision-making: medication selection (avoiding nephrotoxic agents), contrast media protocols (holding contrast or using alternative imaging), or baseline kidney function interpretation. It’s appropriate in nephrology follow-up visits where the patient has returned to baseline creatinine but the prior event is clinically relevant.

Example coding scenario: A patient with resolved AKI from sepsis 4 months ago presents for routine nephrology follow-up with a normal creatinine of 0.9 mg/dL. Coding: Z87.448 as a secondary diagnosis if the prior AKI is clinically referenced. Do not code N17.9. The AKI has resolved; active-condition coding is incorrect.

The acute kidney injury ICD-10 history code question comes up often. Z87.448 is the answer, and it’s exempt from POA reporting on inpatient claims.

Specialty-Specific AKI Coding Workflows: Nephrology, ICU, ER, and Hospital Inpatient

AKI coding looks different depending on where the claim originates. The documentation patterns differ, the CPT codes differ, the claim form differs, and the specificity of the N17.x sub-code selection differs. Here’s how the acute kidney injury ICD-10 coding workflow adapts by specialty.

Nephrology Practice AKI Coding

Nephrology outpatient encounters for AKI management involve a different documentation focus than inpatient presentations. Common scenarios: post-discharge AKI follow-up monitoring creatinine recovery, AKI-on-CKD management, and contrast-induced AKI evaluation. Office E/M levels such as 99214 or 99215 are chosen by medical decision making or by total time on the date of service. See our CPT 99215 high-complexity E/M billing guide for the documentation requirements that support that complexity level.

The G2211 complexity add-on code can apply to longitudinal nephrology care for AKI follow-up when the practitioner is the continuing focal point for the patient’s care or manages a serious or complex condition over time. It isn’t payable when the E/M carries modifier 25, except for a few preventive services. Our G2211 add-on code billing guide covers the full qualification criteria.

ICU and Critical Care AKI Coding

ICU AKI coding is the highest-complexity scenario. The most common presentation is sepsis-induced AKI requiring continuous renal replacement therapy (CRRT). A typical inpatient string is a specific A41 code (such as A41.9) plus R65.20 or R65.21 plus the N17 code, with ICD-10-PCS 5A1D90Z for CRRT (continuous, more than 18 hours per day). Critical care CPT codes 99291 (initial 30 to 74 minutes) and 99292 (each additional 30 minutes; Medicare requires 104 total minutes before the first unit) drive the physician claim.

Documentation focus: hemodynamic instability, vasopressor support, fluid balance over 24 hours, CRRT modality and duration. Unless the provider documents ATN or another necrosis pattern, ICU AKI codes to N17.9, which is a CC, not an MCC. POA indicator is critical: AKI present at ICU admission versus AKI developing during the ICU stay carries different quality reporting implications.

ER AKI Coding

Emergency department AKI presents documentation constraints that inpatient encounters don’t face. The ED workup is rapid, the diagnostic picture is incomplete, and the physician’s documentation window is short. That’s why ED AKI most commonly uses N17.9 (unspecified) as the discharge coding, even when the clinical scenario suggests tubular injury.

E/M coding follows 99281 to 99285 based on MDM complexity. When the same physician sees the patient in the ED and admits them, the admission service generally carries the encounter; a separate ED physician still bills the ED visit. CDI specialists should review ED cases admitted for AKI to refine the N17.x sub-code during the inpatient stay, not wait until discharge.

Hospital Inpatient AKI Coding

Hospital inpatient AKI claims are submitted on the UB-04 claim form with appropriate revenue codes for the care setting. Principal diagnosis selection follows ICD-10-CM Official Guidelines Section II. AHRQ’s PSI 10 measure tracks postoperative AKI that requires dialysis and feeds hospital quality scores.

N17.x as a secondary diagnosis can raise the DRG tier on both surgical and medical DRGs. Accurate POA reporting matters for quality measures, because postoperative AKI that needs dialysis counts against the hospital in PSI 10.

Coding AKI across multiple specialties means juggling different documentation patterns, payer rules, and DRG implications. One O Seven RCM’s coding teams handle nephrology, ICU, ER, and hospital inpatient AKI workflows. Our denial management services catch the documentation gaps before claims hit the payer.

CDI Query Process for AKI Specificity: When and How to Query Providers

CDI query workflows for acute kidney injury ICD-10 specificity are the highest-leverage intervention in the entire coding chain. A compliant query that moves documentation from “AKI” to “acute tubular necrosis” turns an N17.9 into an N17.0 and holds up on audit, because the provider, not the coder, made the diagnosis. The query itself must never mention reimbursement or DRG impact. Here’s when to query and what a compliant query looks like.

When to Query for AKI Specificity

Query the physician when documentation states “AKI” or “acute kidney injury” without specifying the underlying cause, the pathological pattern (tubular, cortical, or medullary), the KDIGO stage, or whether AKI is superimposed on existing CKD. Any one of these missing elements is a CDI query trigger.

Ask concurrent queries while the patient is still in the hospital so the provider can answer before or at discharge. Per the ACDIS/AHIMA Guidelines for Achieving a Compliant Query Practice (2026 Update), every query must be non-leading, must include the clinical indicators that prompted it with their location in the record, and must never mention reimbursement, quality measures, or denial risk.

When physician documentation states AKI without specifying cause or pattern, CDI specialists should query the provider for clarification on (a) the underlying cause (sepsis, dehydration, nephrotoxic agent, contrast media), (b) the pathological pattern (tubular, cortical, or medullary necrosis), and (c) whether the AKI is superimposed on existing CKD.

Query Content Requirements: Compliant Format

A compliant AKI query includes the patient and encounter identifiers, the clinical indicators from the chart that prompted the query (creatinine trend, muddy brown casts on urinalysis, recent contrast administration), and an open-ended or multiple-choice format. Multiple-choice queries need clinically reasonable options plus an “Other, please specify” choice. Yes/no queries are allowed only to confirm a diagnosis already documented or to settle POA, never for a new diagnosis, and they need a third option such as “unable to determine.”

Non-compliant queries include leading language (“Doesn’t this look like ATN?”), single-answer suggestions, or any language that pressures the physician toward a specific code. The 2026 ACDIS/AHIMA query guidelines are the reference for compliant query structure, including queries generated by AI or EHR tools, which must meet the same standards.

Under the 2026 guidelines, concurrent queries should be answered before or at discharge.

Example AKI Query Templates

Template 1: Cause Specificity: Patient was admitted with elevated creatinine (3.2 mg/dL from baseline 0.9 mg/dL) and oliguria. The chart documents “AKI.” Please clarify the underlying cause if known: [ ] Prerenal due to volume depletion [ ] Sepsis-induced [ ] Nephrotoxic medication [ ] Contrast-induced [ ] Other: ___ [ ] Clinically undetermined

Template 2: Pattern Specificity: Patient was diagnosed with AKI with creatinine peak of 4.5 mg/dL and muddy brown casts on urinalysis. Please clarify the pathological pattern: [ ] Acute tubular necrosis (ATN) [ ] Acute cortical necrosis [ ] Acute medullary necrosis [ ] Acute interstitial nephritis [ ] Other: ___ [ ] Clinically undetermined

These templates follow the 2026 ACDIS/AHIMA query guidelines. The clinical indicator in each template (the lab value, the muddy brown cast finding) is what makes the query compliant; it shows the physician exactly what prompted the question without leading toward a specific answer.

Common AKI Coding Errors and Denials: How to Catch Them Before Claim Submission

Six errors come up again and again in acute kidney injury ICD-10 claims. Each one is preventable. Each one is also a pattern, not a one-time mistake. When these errors show up on your remittance reports, they’re showing up across multiple claims to the same payer, not just once.

1. Defaulting to N17.9 when a specific sub-code is documentable. The most common AKI coding error is defaulting to N17.9 when specific physician documentation supports a more precise sub-code. Prevention: build a query workflow that fires when “AKI” appears without sub-code-level language. Denial impact: payer documentation review requests and potential downcoding.
2. Confusing KDIGO Stage with N17 sub-code. As the KDIGO staging section explains, KDIGO Stage 2 does not mean N17.2. The numeric overlap is coincidental. Prevention: separate the two concepts explicitly in coder training. Denial impact: incorrect sub-code may not match clinical documentation, triggering audit flags and medical necessity reviews.
3. Missing the AKI-on-CKD combination. Coding only N17.x when N18.x is also present, or only N18.x when AKI is acute and active, undercodes the clinical picture. Prevention: build a two-check into the coding workflow: does this patient have a CKD history, and is there an acute creatinine change? Both conditions present means both codes required. Denial impact: undercoded severity, lower DRG weight, and potential audit exposure when records show two conditions and claims show one.
4. Incorrect sepsis-AKI sequencing. Coding N17.x as principal when severe sepsis with AKI was present on admission violates Section I.C.1.d of the Official Guidelines. Prevention: check POA first; when severe sepsis was present on admission, the systemic infection code leads. Denial impact: principal diagnosis denial and claim rejection on payers that audit sequencing against guidelines.
5. Reporting N17 as a billable code. N17 is a category header. It’s not billable. Submitting N17 without a sub-code generates an automatic claim rejection. Prevention: configure coder system edits to reject N17 alone at the charge entry level. This one shouldn’t make it past the clearinghouse.
6. Coding AKI from elevated lab values alone without physician diagnosis. Elevated serum creatinine and low eGFR without a physician diagnostic statement don’t support N17.x assignment. Only the physician can diagnose AKI. Prevention: require physician documentation language as a prerequisite for N17.x coding; coders do not infer diagnoses from lab values. Denial impact: medical necessity denial for lack of physician confirmation.

When AKI claims trigger CO-16 missing-information denials, our CO-16 denial code resolution guide walks through the resolution path. When AKI denials accumulate in your AR aging, our AR follow-up services clear the backlog and prevent recurrence.

ICD-11 Transition Outlook: What AKI Coders Should Know

The “acute kidney injury ICD-11” question shows up regularly in CDI team discussions and coder certification prep. Here’s the accurate picture as of October 2026.

The World Health Assembly adopted ICD-11 in 2019, and it took effect globally on January 1, 2022. In ICD-11, acute kidney failure is GB60, and its subcodes classify AKI by stage (GB60.0 to GB60.2 for stages 1 to 3), not by tubular or cortical necrosis. That’s a different logic from ICD-10-CM’s N17 series, which classifies by pathological pattern.

Although the World Health Organization released ICD-11 globally in 2022, the United States continues to use ICD-10-CM in FY 2027 with no adoption rule or implementation date for ICD-11. AKI coding in U.S. healthcare remains within the N17 category of ICD-10-CM through at least the FY 2027 cycle.

HHS hasn’t published a rule or timeline for ICD-11. The National Committee on Vital and Health Statistics asked HHS in 2024 to name a lead office for ICD-11 morbidity coding, and our ICD-11 transition roadmap covers how practices can prepare. Coders should monitor CDC NCHS ICD-10-CM resource announcements. Through at least the FY 2027 cycle (October 1, 2026, through September 30, 2027), AKI coding in US healthcare claims remains within the N17 framework of ICD-10-CM. ICD-11 is not applicable to US billing.

AKI Coding Compliance Checklist for FY 2027

The following compliance checklist consolidates FY 2027 requirements for acute kidney injury ICD-10 coding. CDI specialists, billers, and coding auditors can use this as a daily reference at the point of chart review and claim submission.

Compliance Element	FY 2027 Requirement
Code Edition	FY 2027 ICD-10-CM (effective October 1, 2026, through September 30, 2027)
Primary AKI Code Family	N17.0, N17.1, N17.2, N17.8, or N17.9
Non-Billable Code	N17 alone (category header, not valid for claim submission)
Documentation Keyword	“AKI,” “acute kidney injury,” “ARF,” or “acute renal failure”
Lab Support Required	Serum creatinine trend with dates, BUN, eGFR, urine output
AKI vs CKD Distinction	Acuity language required for N17.x; chronic timeline (3+ months) for N18.x
Sepsis + AKI Sequencing	When severe sepsis is POA: systemic infection code first, then R65.20 or R65.21, then the localized infection and N17.x (Section I.C.1.d)
AKI on CKD Coding	Both N17.x AND N18.x required (plus I12.-/I13.- or E08.22 to E13.22 when documented); N17.x sequences first when acute is primary
Contrast-Induced AKI	N17.0 (if ATN documented) or N17.9 + T50.8X5A + N14.11 (if contrast-induced nephropathy documented)
Drug-Induced AKI	N17.x + appropriate T-code (T36-T50 series) with correct 7th character
Rhabdomyolysis-Induced AKI	M62.82 + N17.9 (N17.0 only if ATN documented); T79.6XXA if traumatic
Hepatorenal Syndrome	K76.7 + N17.x (only if AKI explicitly documented by physician)
Dehydration-Induced AKI	N17.x + E86.0 (dehydration) or E86.1 (hypovolemia)
History of Resolved AKI	Z87.448 (when AKI is resolved and no longer actively treated)
MCC Designation	N17.0, N17.1, N17.2 = MCC; N17.8, N17.9 = CC (MS-DRG v44)
POA Indicator	Required on inpatient claims (Y, N, U, or W); Z87.448 is POA exempt
Avoid	“Renal insufficiency” without acuity language, lab values without physician diagnosis, KDIGO Stage number as N17 sub-code proxy

Per the CMS MS-DRG Definitions Manual (v44), N17.0, N17.1, and N17.2 are MCCs and N17.8 and N17.9 are CCs. Review this checklist at chart review. One missed element is all it takes for a payer to downcode or request clinical documentation.

When to Outsource AKI Coding to a Specialty RCM Partner

There’s no universal answer to whether acute kidney injury ICD-10 coding should be handled in-house or outsourced. The decision depends on claim volume, staff expertise, denial rate, and the complexity of the specialty mix you’re managing. Here’s a practical framework.

In-house coding makes sense when you’re a single-specialty practice with modest AKI claim volume, when you have certified coders on staff with active nephrology or critical care experience, when physician documentation consistently meets specificity requirements without regular CDI intervention, and when your AKI-related denials stay low. That scenario is relatively rare across the practices we work with, but it exists.

Outsourcing makes financial sense when you’re managing multi-specialty groups with high AKI claim volume across nephrology, ICU, and hospital inpatient simultaneously. When AKI-related denials keep showing up on your remits. When you’re managing complex DRG-driven inpatient workflows where CC and MCC capture decisions are made under time pressure. When you’re launching new nephrology providers who need credentialing and coding support simultaneously (see our credentialing and contracting services for the enrollment side of that workflow). When payer-specific compliance audits or LCD updates are affecting your AKI claim acceptance. Or when N17.9 default-coding patterns have already cost you measurable revenue.

The decision is rarely all-or-nothing. Hybrid models work for many practices: in-house CDI with outsourced coding review, or in-house outpatient coding with outsourced inpatient DRG optimization. The right partnership depends on volume, complexity, and existing workflow maturity.

Ready to stop losing AKI revenue to documentation gaps and unspecified-code defaults? One O Seven RCM’s certified coding team works nephrology, ICU, and hospital inpatient AKI claims across the full N17 family. We catch the specificity gaps, sequence the comorbid scenarios correctly, and protect your DRG assignments. Contact our team for an AKI coding audit and denial-rate analysis.

Final Thoughts for Healthcare Providers and RCM Teams

Accurate AKI coding under FY 2027 ICD-10-CM is more than picking N17.9 and moving on. It’s the disciplined application of the full N17 family, KDIGO clinical alignment, sepsis sequencing rules, and DRG-aware documentation. The practices that get this right protect revenue and patient-care quality records simultaneously. The ones that default to N17.9 out of habit give up MCC capture and audit defense.

The final KDIGO 2026 AKI/AKD Guideline, still in preparation after public review closed in May 2026, will likely change clinical definitions and CDI query triggers. Coding teams that anchor on international clinical authority alongside the US ICD-10-CM standard will adapt fastest when that guideline finalizes. Watch both KDIGO and CMS and NCHS announcements.

The N17 category, the FY 2027 effective dates and CC/MCC split, and the KDIGO 2026 update form the reference points for accurate AKI coding through the next fiscal cycle. Practices that train their coders on these three anchors and apply them consistently across nephrology, ICU, ER, and hospital inpatient settings will get the most accurate DRG assignments under the current code set.

Frequently Asked Questions: AKI ICD-10 Coding

What is the ICD-10 code for acute kidney injury?

The most commonly assigned ICD-10-CM code for acute kidney injury is N17.9 (Acute kidney failure, unspecified), used when the underlying cause and pattern are not documented. The full N17 series includes N17.0 (with tubular necrosis), N17.1 (with cortical necrosis), N17.2 (with medullary necrosis), N17.8 (other), and N17.9 (unspecified). All five are billable; N17 alone is the non-billable category header.

Is acute kidney injury the same as kidney failure?

Acute kidney injury and acute kidney failure are clinically synonymous in modern nephrology. Both describe a rapid decline in kidney function over hours or days. In ICD-10-CM, both terms code to the N17 category. AKI became the preferred term after the AKIN criteria of 2007 and KDIGO 2012, but ARF remains acceptable documentation language for coding purposes.

What is another name for acute kidney injury?

Acute kidney injury is also called acute renal failure (ARF) and acute kidney failure, and all three terms code to the N17 category in ICD-10-CM. “Acute renal insufficiency” is different: the ICD-10-CM Index sends it to N28.9, so query the provider if that’s the only term in the chart. AKI is the preferred current term per KDIGO 2012 Clinical Practice Guideline; older charts may use ARF interchangeably without coding consequence.

What is the diagnosis of acute kidney injury?

Acute kidney injury is diagnosed per KDIGO 2012 criteria when one of the following is met: serum creatinine increase of 0.3 mg/dL or more within 48 hours, serum creatinine increase to 1.5 times baseline within 7 days, or urine output less than 0.5 mL/kg per hour for 6 hours. Physician diagnostic documentation is required for ICD-10-CM N17.x assignment; lab values alone don’t support the code.

What is the difference between N17.0 and N17.9?

N17.0 (Acute kidney failure with tubular necrosis) applies when physician documentation explicitly states acute tubular necrosis or ATN. N17.9 (Acute kidney failure, unspecified) applies when AKI is documented but the pathological pattern and cause are not specified. N17.0 is an MCC under MS-DRG v44, while N17.9 is a CC, so documented ATN can move an inpatient case to a higher DRG tier.

What is the ICD-10 code for AKI on CKD stage 3?

AKI on CKD stage 3 requires two codes: the appropriate N17.x code (typically N17.9 if cause is undocumented) plus either N18.31 (CKD stage 3a) or N18.32 (CKD stage 3b) depending on physician documentation. Both codes are required to capture the acute-on-chronic condition. The N17.x code sequences first when the acute event is the reason for the encounter.

Can AKI and CKD be coded together?

Yes. When acute kidney injury is superimposed on chronic kidney disease, both N17.x and the appropriate N18.x stage code must be reported. The acute condition (N17.x) is sequenced first when it is the reason for the encounter. This is the acute-on-chronic kidney disease presentation, and submitting only one code significantly undercodes the clinical severity.

Is N17.9 billable?

Yes. N17.9 (Acute kidney failure, unspecified) is a billable ICD-10-CM code in FY 2027 and a CC (not an MCC) under MS-DRG v44. It’s valid on inpatient and outpatient claims when physician documentation supports AKI without specifying cause or pattern. However, N17.9 should be used as a last resort; when physician documentation supports a specific N17 sub-code, the more specific code is required.

What is the ICD-10 code for history of AKI?

Z87.448 (Personal history of other diseases of urinary system) is the ICD-10-CM code for resolved acute kidney injury that is no longer being actively treated. Z87.448 replaces the active N17.x code once AKI has resolved and is reported as a secondary diagnosis on encounters where prior AKI is clinically relevant to current management decisions.

How do you code AKI with sepsis?

Per ICD-10-CM Official Guidelines Section I.C.1.d, when AKI is caused by sepsis, the underlying infection code (e.g., A41.9 unspecified sepsis or A41.51 E. coli sepsis) is sequenced first, followed by R65.20 (severe sepsis without septic shock) or R65.21 (severe sepsis with septic shock), then the appropriate N17.x code as a secondary diagnosis. This applies when severe sepsis is present on admission; if it develops after admission, the condition that led to the admission stays principal.