CO 226 means the payer asked the billing or rendering provider for information and did not receive it, did not receive it in time, or found what arrived incomplete. The CO prefix stands for Contractual Obligation, so the provider absorbs the adjustment and cannot bill the patient for it.
Key Takeaways
- CARC 226 is a Claim Adjustment Reason Code, not a remark code, and billing teams confuse the two often on the remittance.
- X12 requires at least one remark code alongside it, and that companion code names the specific missing item.
- The CO 226 denial code is a soft denial, which means no one judged the service on its merits and you can reopen the claim in most cases.
- Medicare prepayment documentation requests carry a 45-day response window, and the claim denies on day 46 without a usable response.
This guide covers CARC 226 from the X12 description through the payer-specific edits most billing teams miss.
What Is the CO 226 Denial Code?
The Official X12 Description of CARC 226
X12, the standards body chartered by the American National Standards Institute that maintains every HIPAA-mandated claim adjustment reason code, defines CARC 226 this way on its X12 Claim Adjustment Reason Codes list:
“Information requested from the Billing/Rendering Provider was not provided or not provided timely or was insufficient/incomplete. At least one Remark Code must be provided (may be comprised of either the NCPDP Reject Reason Code, or Remittance Advice Remark Code that is not an ALERT.)”
Check three dates and you’ll see how stable this code is. X12 gave CARC 226 a start date of September 21, 2008, and last modified the wording on July 1, 2013.
External Code List 139, the CARC list itself, was last modified November 1, 2025. That list moved recently, though the code inside it did not.
CARC 226 also took over part of deactivated CARC 17, which stopped July 1, 2009. X12 split that code by owner, so 226 and 227 exist as a matched pair.
What the CO Group Code Means for Your Money
CO is one of five claim adjustment group codes in the X12 standard. It sits in front of the reason code on every adjustment line and answers one question: who absorbs the balance. All five appear on the X12 Claim Adjustment Group Codes list:
- CO: Contractual Obligation
- PR: Patient Responsibility
- PI: Payer Initiated Reductions
- OA: Other Adjustment
- CR: Corrections and Reversal, not used with 005010 and up
The group code decides who absorbs the balance, and the reason code explains what went wrong.
Where CO 226 Appears on the 835 and the EOB
On the 835 electronic remittance advice, the group code sits in CAS01 and the reason code sits in CAS02. A paper EOB prints the same pairing in the adjustment or denial reason column.
The remark code arrives separately, and it names the missing item. Read all three fields before you touch the claim.
Is 226 a Reason Code or a Remark Code?
226 is a reason code, not a remark code. It’s a Claim Adjustment Reason Code, and it gives you the category of problem. The remark code traveling with it is a separate code, and that one names the missing item.
Billers search for co226 remark code and co226 reason code interchangeably, which is how the confusion spreads. One denial code co226 line carries three codes at once, and each answers a different question.
CARC, RARC, and Group Code: What Each One Tells You
| Code type | Example on this denial | What it tells you |
|---|---|---|
| Claim Adjustment Group Code | CO | Who absorbs the balance |
| Claim Adjustment Reason Code (CARC) | 226 | The category of problem |
| Remittance Advice Remark Code (RARC) | N706, M127, N517 | The specific item that’s missing |
The remark code narrows the category into an action, which is the same reading discipline that makes a CO-16 missing information denial resolvable.
One more correction while we’re here. CARC 226 is not an error code and it is not a rejection. The payer adjudicated the claim and then applied an adjustment to it.
That distinction changes your correction path. A rejection stopped short of adjudication, so you fix the file and send it again. An adjudicated denial carries a claim number, and the payer expects a response tied to it.
CO 226 vs. PR 227 vs. CO 16 vs. CO 252
All four codes below describe a claim the payer couldn’t adjudicate for want of information. They aren’t interchangeable. The difference comes down to who owed the information and what form it takes, and picking the wrong one sends the claim down the wrong correction path.
CO 226 vs. PR 227 vs. CO 16 vs. CO 252: How to Tell These Denials Apart
| Code | Who owed the information | X12 description | Your next move |
|---|---|---|---|
| CO 226 | The billing or rendering provider | Information requested from the Billing/Rendering Provider was not provided or not provided timely or was insufficient/incomplete | Send exactly what the payer asked for, the way they asked for it |
| PR 227 | The patient, insured, or responsible party | Information requested from the patient/insured/responsible party was not provided or was insufficient/incomplete | Contact the member. The information is not yours to supply |
| CO 16 | Nobody. The claim itself was incomplete | Claim/service lacks information or has submission/billing error(s) | Correct the claim data and resubmit |
| CO 252 | The provider, specifically an attachment | An attachment/other documentation is required to adjudicate this claim/service | Attach the document and resubmit |
A pr-227 denial code shifts the balance to the member, which follows the same PR group code patient liability logic that governs every patient-responsibility adjustment. Chasing the chart on a 227 wastes the window, because the payer is waiting on the patient.
Why CO 226 and PR 227 Get Reversed
Both codes started on the same day, September 21, 2008, and both replaced deactivated CARC 17, which covered requested information without naming who owed it. X12 split code 17 by owner: 226 went to the provider side and 227 went to the member side.
Sequential numbers, near-identical wording, one word of difference that changes the entire workflow. Two published guides still carry the pair backwards, which is how the error keeps circulating.
Treat a 226 like a 227 and your staff calls the patient for records the payer asked you for. The response window closes while your team waits on the wrong person.
The 227 denial code isn’t the only near neighbor worth separating out. CO 252 sits equally close, and the difference there is the attachment itself, covered in the CO-252 documentation attachment denial guide.
Four Common Definitions of CO 226 That Are Wrong
Search results for this code carry several conflicting definitions. Anyone looking up the co 226 denial code meaning will hit at least two of them on the first page. Each common wrong answer below is the correct definition of a different CARC.
Four Wrong Definitions of CO 226 and the Codes They Describe Instead
| What you may have read | What that describes instead | Verified code |
|---|---|---|
| CO 226 means information was requested from the patient or insured party | The member-side request code | CARC 227 |
| CO 226 means the provider is out-of-network or non-participating | The network-status code | CARC 242 |
| CO 226 means duplicate services or charges | The duplicate claim code | CARC 18 |
| CO 226 means the secondary payer never got the primary EOB | The coordination of benefits code | CARC 22 |
Every assignment above traces back to the live X12 list. CARC 242 reads “Services not provided by network/primary care providers.” Duplicates belong to CARC 18, which reads “Exact duplicate claim/service” and drives the CO-18 duplicate claim denial workflow.
Coordination of benefits belongs to CARC 22, which reads “This care may be covered by another payer per coordination of benefits” and routes through CO-22 coordination of benefits instead. The co-226 denial code has one definition, and X12 publishes it.
Each wrong definition sends a workqueue somewhere useless. Chase a duplicate that isn’t there and the records request sits unanswered while the window runs. A network-status hunt opens a contracting ticket for what was only ever a documentation gap.
If a remittance shows CO 226 and your team is working any of the four problems above, you’re fixing the claim against the wrong code.
Which Remark Codes Appear With CO 226
X12 requires at least one remark code with every CARC 226. That remark code is the only part of the remittance that names the missing item. Work a co 226 denial code n517 pairing without reading the RARC and you’re guessing, and a wrong guess produces a second 226.
Remark Codes That Appear With CO 226 and What Each One Requires
| Remark code | What it means | What to send |
|---|---|---|
| M127 | Missing patient medical record for this service | The complete record for the date of service |
| N706 | Missing documentation | The specific document named in the payer’s request |
| N517 | Resubmit a new claim with the requested information | A new claim, not an appeal |
| N767 | Provider must be enrolled in the member’s Medicaid state program | An enrollment or revalidation fix, then rebill |
| N831 | Provider or supplier enrollment revalidation incomplete | Complete revalidation before resubmitting |
| N258 | Billing provider address cannot be a PO Box | A corrected physical service address |
| N10 | Adjustment based on a review organization or manual adjudication | Follow the payer’s stated review response path |
| N225 | Incomplete or invalid documentation, orders, notes, summary, report, or chart | The complete and legible version of what was sent |
Sourcing note. M127, N706, N517, and N225 are general RARC descriptors that any payer may use. The n706 denial code description and the n517 denial code description both carry across the industry.
The rest are payer-specific pairings. N767 appears in Ohio Medicaid managed care guidance for PNM enrollment denials, N831 in Louisiana Department of Health guidance for incomplete revalidation, N258 in a Texas managed care crosswalk as a PO Box address edit, and N10 in the MassHealth CARC and RARC change log.
Read the Remark Code Before You Touch the Claim
The RARC decides the lane. A documentation message means you assemble the records and send them. If the message points at enrollment, fix the provider file first, because a clean claim against a lapsed enrollment produces the same denial again.
N517 is the odd one out. It asks for a new claim rather than an appeal, and filing the appeal instead adds weeks to a claim that had a faster route available. Read the remark code before you open the chart.
Verify the Remark Code Against the Current List
RARC descriptors change. The CARC list was last modified November 1, 2025, but CMS maintains the RARC list separately and it changes more often. Older billing guidance circulating online still cites remark code descriptions that have since been revised or retired.
Check the live X12 Remittance Advice Remark Codes list before you act on an unfamiliar RARC, and log the retrieval date in your denial notes. The co-226 denial code description stays put while the companion codes shift underneath it.
Why CO 226 Denials Happen
Almost every 226 denial code starts the same way. The payer sent a request, and either no one answered it or somebody answered the wrong question. In most cases the service itself was payable, and the claim stalled before anyone reviewed the medicine.
- The request went somewhere no one watches. (Mailroom and correspondence) Records requests go to the address or fax number the payer has on file, which is often an address your practice left two moves ago.
- The request landed in an unowned queue. (Billing operations) A correspondence inbox with no named owner and no service level lets the response window close without anyone noticing.
- The response answered the wrong question. (Billing and clinical) The payer asked for one operative note and somebody sent the whole chart. Payers treat a non-responsive answer the same as no answer.
- The documentation went the wrong way. (Billing operations) Portal upload, a cover sheet, or a designated fax line are often required before the payer matches records back to the claim.
- The provider file was the problem, not the paperwork. (Credentialing) Enrollment lapses and incomplete revalidation surface as CARC 226 in several state Medicaid programs. No clinical documentation clears that one.
That last trigger is the one most co 226 denial code descriptions leave out, and it sends teams chasing records for a problem sitting in the credentialing file.
Every trigger here is a process failure with a clock attached, and that clock runs shorter than teams assume.
Payer-Specific CO 226 Edits You Should Know
The X12 descriptor is national. Payer-level usage of CARC 226 is not. Several state Medicaid programs attach it to provider enrollment problems that have nothing to do with clinical documentation, and a team sending medical records against those edits will get the same denial back.
How Four State Programs Use CARC 226
| Payer or program | Paired remark code | What it means there |
|---|---|---|
| Ohio Medicaid managed care | N767 | Billing or rendering provider is not enrolled and active in PNM. If the claim was already paid, recoupment is not permitted for this scenario |
| Louisiana Medicaid | N831 | Provider revalidation is incomplete. Applies to pharmacy, prescriber, billing, rendering, referring, and ordering records |
| Texas managed care | N258 | Billing provider address cannot be a PO Box |
| MassHealth | N10 | Adjustment based on the findings of a review organization or manual adjudication |
Read that table with a workqueue in mind. CARC 226 covers at least four operationally distinct problems wearing one code: a documentation gap, an enrollment gap, a provider-file mismatch, and an address-format edit. A single response template can’t route all four.
Anyone working co 226 denial code medical billing across state lines runs into this fast. The same code on an Ohio remittance and a Texas remittance can point at two unrelated fixes, and the RARC is the only field that separates them. Sort your 226 volume by payer before you sort it by anything else.
Ohio Department of Medicaid states the PNM enrollment rule in its Ohio Medicaid PNM enrollment policy guidance. The revalidation pairing comes from the Louisiana Medicaid provider FAQ. Both govern those programs and neither establishes a universal pairing.
Two of the four rows above are credentialing problems rather than billing problems. Enrollment lapses and incomplete revalidation put the denial on the claim, but the fix lives in the provider file, which puts provider credentialing and revalidation inside your denial code co-226 workflow.
Resubmit without clearing the enrollment gap and you get the identical denial back. Ohio’s guidance also bars recoupment on an already-paid claim in that scenario, which is a specific right your team can act on.
Is CO 226 Patient Responsibility?
No. CO 226 is a contractual obligation, which means the provider absorbs the adjustment. You cannot transfer that balance to the patient.
The group code decides liability, not the reason code. CO assigns the balance to the provider under the payer contract. For Medicare, CMS instructs that providers are prohibited from billing the beneficiary for amounts reported under a CO group code, and that rule sits alongside the broader contractual obligation write-off rules your posting team already applies.
One distinction matters more than any other here, and few pages publish it. The same reason code can arrive with a different group code.
A remittance showing pi 226 denial code instead of CO 226 tells you the payer classified the adjustment as a payer-initiated reduction. The reason stays identical while the liability assignment changes. Teams hunting an oa 226 denial code description are looking at the same CARC under a fourth group code.
Every co 226 denial code reimbursement decision comes down to one field. Check CAS01 before you write anything off or bill anything out.
The Medicare ADR Clock: 45 Days, Then the Claim Denies
What an ADR Is and Why It Produces a 226
Medicare contractors pull the record behind a claim before deciding whether it survives review. A Medicare Administrative Contractor, a Recovery Audit Contractor, a Supplemental Medical Review Contractor, or a Unified Program Integrity Contractor can each issue one.
An Additional Documentation Request asks for the paperwork behind a claim the payer holds, so the adjustment carries a code about information rather than coverage. It arrives as a letter or portal notification, and the claim pends while the contractor waits.
The claim denies once that window closes, and CARC 226 lands on your remittance. Any co 226 denial code solution has to start earlier than that.
Medicare ADR Response Windows
- MAC prepayment and post-payment review: 45 calendar days
- RAC and SMRC review: 45 calendar days
- UPIC review: 30 calendar days
- Claims deny by day 46 when no response arrives
- Contractors may accept a late response for good cause if you ask before the deadline
Both windows appear in CMS Additional Documentation Request guidance, and the 45-day rule is confirmed at contractor level in the Noridian ADR response requirements. Contractors publishing medical review results list non-response as a leading denial reason.
Why Teams Miss the Window
By the time the denial shows up on the remittance, a chunk of the window is gone. The letter went out weeks earlier, and if it landed in a shared inbox or an unmonitored fax line, no one started a clock.
Billing teams find out about the request and the denial in the same moment. Appeal volume won’t close that gap.
An ADR response isn’t a resubmission. It has to answer the specific request, arrive through the channel the contractor named, and match back to the claim.
Every ADR response and denial recovery package our team builds gets audited against the criteria cited in the request. A package answering the wrong question fails the same way a missing one does.
If your ADR responses get built after the denial arrives rather than before, that’s a workflow gap, and most teams close it in one cycle.
How to Fix a CO 226 Denial
- Pull the complete remittance, not only the denial line. Record the claim number, service date, adjusted line, group code, CARC 226, every RARC, and any claim-level message. If the remark code is missing from what you can see, get the full 835 before you decide anything.
- Find the original request. The RARC gives you the category. Your payer’s letter or portal message carries the exact ask, the deadline, and the submission channel. Working from the RARC alone means guessing at the specifics.
- Confirm who owed the information. Provider-side requests belong to you. If the remark points at enrollment or a provider-file mismatch, the fix sits in the credentialing record, and no clinical documentation will clear it.
- Send exactly what the payer asked for, nothing more. Sending the whole chart when the payer asked for one operative note gets treated as a non-response. Confirm the documentation is complete, legible, dated, and signed before it leaves.
- Use the channel the payer named. Portal upload, a claim-specific cover sheet, or a designated fax line are often required for records to match back to the claim. Correct documents sent the wrong way get lost.
- Track the confirmation and check the next remittance. Log the submission date, the confirmation or correspondence ID, and the follow-up owner. Confirm whether 226 cleared or whether a different adjustment replaced it.
Corrected Claim, Records Response, or Appeal?
Three lanes exist and only one of them fits any given co226 denial code. The remark code tells you which.
Corrected Claim, Records Response, or Appeal: How to Route a CO 226
| What the remark code indicates | Correct lane | Why |
|---|---|---|
| A specific document is missing | Records response through the payer’s stated channel | The claim is waiting on paperwork, not a decision |
| N517, resubmit with the requested information | New or corrected claim | The payer is asking for a fresh submission, not an appeal |
| The response window already closed | Appeal, with the documentation attached | Records submission is no longer available. Explain why the original request went unanswered |
Name the artifacts as you go. The ICN on the denial, the esMD or portal confirmation, and the cover sheet number are what let a payer rep find your submission on a status call.
Appeal when the payer wants records, or resubmit after the window has closed, and you burn time the claim doesn’t have. Effective payer-specific appeal management starts with the remark code rather than the appeal form, and the co 226 denial code descriptions on your ERA carry everything you need to pick the lane.
CO 226 Appeal and Filing Deadlines
Two different clocks run on a denial code co 226, and confusing them costs claims. The response window is how long you have to answer the original information request. Your appeal window starts later, after the denial posts.
CO 226 Response and Appeal Windows by Clock Type
| Clock | Payer type | Window |
|---|---|---|
| Response to a documentation request | Medicare, MAC prepayment or post-payment review | 45 calendar days |
| Response to a documentation request | Medicare, UPIC review | 30 calendar days |
| Appeal after denial | Medicare redetermination | 120 days from the date of the initial determination notice |
Most competitor pages publish a single commercial appeal range and cite nothing for it. Three of them contradict each other on the same page of search results, which tells you the number was copied rather than verified.
Commercial payer windows vary by payer and often by plan inside the same payer. Published ranges circulating online differ widely and carry no source behind them.
Check the appeal window in your contract or on the denial notice itself rather than relying on a general range. A number you can’t trace is worse than no number at all, because your team will build a real deadline around a figure no one verified.
What a CO 226 Looks Like on a Remittance
A CO 226 line carries four pieces of information, and the order you read them in matters. Take them out of order and you’ll fix the wrong thing. The example below is the electronic version, where the pairing shows up first.
CAS*CO*226*[adjustment amount] LQ*HE*N706
Read it in this order:
- CAS01 = CO. The provider absorbs the balance. Do not bill the patient.
- CAS02 = 226. The payer requested information and did not get a usable response.
- CAS03 = the adjusted amount. The dollars at risk on this line.
- RARC = N706. Missing documentation. This is the only part that names the item.
On the ERA the pairing reads co226 with no space, which is how most billing systems store it. A paper EOB prints the same information in the denial reason column as CO-226 followed by the remark code.
On paper the pairing often appears as one string, which is how most billers first meet it. Teams typing c0226 with a zero are looking at this same line.
Group code first, reason code second, remark code third, and the remark code is where the work starts.
How to Prevent CO 226 Denials
The strange part about this denial is that the documentation is already sitting in the chart. Somebody performed the service, somebody wrote the notes, and the claim went out clean. The handoff between the payer asking and a person answering is the piece that broke.
- One owned correspondence queue. A named owner and a stated service level, not a shared inbox four people check when they remember.
- Verified request addresses on file with every payer. Confirm the mailing address and fax number each payer holds for records requests, and update them after a move or acquisition.
- A request log tied to the claim. Every incoming records request gets logged against its claim with a due date, so an unanswered one surfaces before the window shuts.
- Current provider enrollment and revalidation status. Enrollment lapses surface as claim denials in several state Medicaid programs, and the front-end discipline that prevents CO-197 prior authorization denials prevents these too.
- Denial tracking by payer, remark code, and provider role. Tracking co 226 in aggregate tells you nothing. Break it out by RARC and provider to see which handoff broke.
Once a co 226 denial code passes its response window, the records lane closes and an appeal is the only route left.
At that point the claim moves into aged AR recovery services, where the fix is an appeal package rather than a records response.
CO 226 Denial Code: Frequently Asked Questions
What Does Denial Code CO 226 Mean?
The co 226 denial code means the payer requested information from the billing or rendering provider and did not receive it, did not receive it in time, or found what arrived incomplete. Because the CO group code assigns the balance to the provider, the patient cannot be billed for it.
The reason code gives you the category. Its companion remark code names the specific document, enrollment record, or address the payer is missing, and that companion code is where the real work starts.
Is 226 a Denial Code or a Remark Code?
Denial code 226 is a Claim Adjustment Reason Code, not a remark code. Three codes appear on the same remittance line: the group code CO assigns liability, the reason code 226 gives the category, and the remark code such as N706, M127, or N517 names the missing item.
Teams that stop reading at 226 end up guessing. The remark code is the actionable element, and X12 requires at least one of them on every 226 adjustment, so a remittance without one is incomplete.
What Is the Difference Between CO 226 and PR 227?
CO 226 is provider-side and PR 227 is member-side. Both codes started September 21, 2008, and both replaced deactivated CARC 17, which covered requested information without naming who owed it. X12 split the old code by owner, and that ownership question is the only difference between them.
Confusing the two costs the response window. A team that treats a 226 like a 227 calls the patient for records the payer asked the practice to supply, and the deadline passes while the claim sits in a queue no one is watching.
Can I Bill the Patient for a CO 226 Denial?
No. CO 226 carries the Contractual Obligation group code, so the provider absorbs the adjustment and the balance cannot move to the patient. For Medicare, CMS instructs that providers are prohibited from billing the beneficiary for amounts reported under a CO group code.
Read the group code before any balance decision. The same reason code can arrive as a pi 226 denial code, which is a payer-initiated reduction rather than a contractual one, and CAS01 is the field that tells you which one you’re holding.
Which Remark Codes Appear With CO 226?
M127 means the payer wants the complete medical record for that date of service. Missing documentation shows up as N706. N517 asks for a new claim rather than an appeal, while N767 flags Medicaid enrollment status and N831 flags incomplete revalidation.
Some of those pairings are payer-specific rather than universal. N767 comes from Ohio Medicaid managed care guidance and N831 from Louisiana, so check the current X12 remark code list before acting on an unfamiliar co226 denial code description.
How Long Do I Have to Respond to a CO 226?
Medicare gives you 45 calendar days to answer a MAC prepayment or post-payment documentation request, and 30 calendar days for a UPIC review. Claims deny by day 46 when no usable response arrives. A Medicare redetermination runs 120 days from the initial determination notice.
Commercial windows vary by payer and often by plan inside the same payer. Published ranges circulating online carry no source, so pull the window from your contract or the denial notice itself.
Should I File a Corrected Claim or an Appeal?
The remark code decides. A request for a specific document routes to a records response through the payer’s stated channel. N517 routes to a new or corrected claim. A response window that already closed routes to an appeal with the documentation attached.
Picking the wrong lane costs weeks. Appealing when the payer wants records leaves the original request unanswered, and resubmitting after the window has closed puts a fresh claim up against a deadline that already passed.
Does CO 226 Always Mean Documentation Is Missing?
No. Several state Medicaid programs use CARC 226 for provider enrollment and revalidation problems that carry no documentation component at all. Ohio pairs it with N767 for PNM enrollment gaps, and Louisiana pairs it with N831 for incomplete revalidation.
The fix location changes with the cause. An enrollment-driven 226 gets resolved inside the provider file, and resubmitting the claim before that record is current returns the identical denial every time.
Working CO 226 Denials at Scale
One 226 is a paperwork problem. A pattern of them is a diagnostic. Cluster your co 226 denial code volume by payer, remark code, and provider role, and the pattern names the broken handoff for you.
Concentrated under one payer points to a bad address on file. A single provider carrying most of the volume points to an enrollment gap. One service line generating them points to a documentation template that doesn’t carry what that payer requires.
These age out for a reason that has nothing to do with effort. The request and the denial arrive in different places at different times, and no one owns the gap between them. Practices that fix this assign the correspondence queue instead of adding appeal hours.
If your CO 226 volume is concentrated somewhere and no one has looked at where, that’s a 90-day denial pattern worth pulling. We do that review at no cost, and you’ll know within a week whether the problem is an address, an enrollment record, or a documentation template.
