PR-31 Denial Code: What “Patient Cannot Be Identified as Our Insured” Means and How to Fix It (CO-31 Included)

The PR 31 denial code means the payer looked for your patient and couldn’t find a matching insured record. X12 words reason code 31 as “Patient cannot be identified as our insured.” The same code shows up as CO-31, and those two letters decide who owes the balance.

Code 31 says nothing about medical necessity, coding, or plan benefits. It says the identifiers on your claim didn’t match the payer’s enrollment file. That’s why a corrected resubmission clears most of them and an appeal usually doesn’t.

Key takeaways

• PR-31 and CO-31 are the same reason code, CARC 31: “Patient cannot be identified as our insured.”
• The group code decides liability. PR points the balance at the patient, CO keeps it with the provider.
• Most 31s trace to a member ID, name, date of birth, or subscriber mismatch, or a claim sent to the wrong payer.
• You clear it by correcting the identifiers and resubmitting.
• Medicare posts it as PR-31. An invalid MBI comes back as CO-16 with N382 instead.

Your team might type it as PR31, PR 31, CO31, or denial code PR31. On the remittance it’s always reason code 31 with a group code in front.

What Is the PR-31 Denial Code (and CO-31)?

PR-31 denial code is Claim Adjustment Reason Code 31 from the X12 code list, posted with the group code PR, and it means the payer’s enrollment system found no insured member matching your claim.

Every adjustment on a remittance carries two parts. The two letters are the Claim Adjustment Group Code, which assigns financial responsibility. The number is the Claim Adjustment Reason Code, or CARC, which gives the reason. A Remittance Advice Remark Code, or RARC, adds detail on top of the CARC.

PR-31 Denial Code Description: The Official X12 Wording

“Patient cannot be identified as our insured.”

X12 gave code 31 a start date of January 1, 1995 and last modified that wording on September 30, 2007. The list your payer works from is the November 1, 2025 version, and X12 marked the CARC list Status Last Reviewed on August 1, 2026.

That pr 31 denial code description is older than most billing software your practice has run, and it still describes what payers mean today.

Say a patient, call her Maria Garcia, hands the front desk a card reading W123456789. Your team keys W123456798. The payer searches, finds nobody, and the line comes back CAS*PR*31. Maria has coverage. Your claim described someone who doesn’t exist.

Not Recognized and Not Eligible Are Different Denials

Payers reach for other codes when they know the member and the timing fails: 26 for expenses before coverage, 27 for expenses after termination, 200 for a lapse in coverage. Denial code 31 means the search came up empty.

X12 settled this in RFI 1423. Claim status code 4 on the 835 applies only when the payer doesn’t recognize the patient or subscriber and hasn’t forwarded the claim. Once the payer finds the member, it reports the claim as processed, even when it pays zero.

A 31 tells you the lookup failed, which means your job is to make the lookup succeed.

PR-31 vs CO-31: Which Group Code You Got and Who Pays

CO-31 and PR-31 are the same reason code with different liability. CO stands for Contractual Obligation and keeps the unpaid balance with the provider. PR stands for Patient Responsibility and points it at the patient.

Same denial, different follow-up. A PR-31 can turn into a patient statement once you confirm the patient had no coverage that day. A CO-31 stays a provider problem until someone fixes the claim.

CO 31 Denial Code Descriptions by Group Code

Medicare is blunt about this. CMS states that beneficiaries may be billed only when Group Code PR is used with an adjustment, and Noridian warns suppliers that billing a beneficiary for amounts outside PR can bring penalties. Read the group code before anyone touches the patient’s account.

Commercial contracts and state law decide the rest. Treat a co-31 denial code balance as a write-off only after you’ve corrected the claim and the payer still can’t find the member. Hold every patient statement on a PR-31 until eligibility backs you up.

That co 31 denial code description reads the same as PR-31 on the EOB, which is where teams get caught. With 27 the payer knows the member and tells you coverage ended, and our PR-27 coverage terminated guide walks that workflow. A 31 means the payer can’t find the member at all.

How Denial Code 31 Appears on the 835 ERA and EOB

Denial code 31 shows up on the 835 inside a CAS segment, with the group code first, the reason code second, and the adjusted dollars third.

CLP*ACCT10422*4*185.00*0*185.00*CI*P26091100442*11~

CAS*PR*31*185.00~

NM1*QC*1*GARCIA*MARIA****MI*W123456798~

Those values are illustrative. CLP02 carries 4, the claim status X12 reserves for a patient or subscriber the payer doesn’t recognize. CAS01 holds the group code and CAS02 holds the reason code, which is where your software gets the label PR-31.

The NM1*QC line names the patient the payer failed to match. A paper EOB prints the same event as reason 31 with PR or CO beside it.

Is There a Remark Code 31? CARC 31 vs RARC N31 and MA31

There is no remark code 31. The number 31 belongs to the reason code list, and the look-alike remark codes are N31, “Missing/incomplete/invalid prescribing provider identifier,” and MA31, “Missing/incomplete/invalid beginning and ending dates of the period billed.”

Searching the remark list for a 31 sends a biller after the wrong field.

Remark Codes That Ride With CARC 31

Column two below carries the official wording from the X12 Remittance Advice Remark Codes list.

Medicare adds a twist worth knowing. Since CMS Transmittal R4047CP, MACs use N382 in place of MA61 for patient identifier problems and pair it with CO-16 rather than 31. A bad MBI comes back as CO-16 with N382, and our CO-16 remark code pairings guide covers that path. A valid MBI that matches no entitled beneficiary comes back as PR-31.

Which RARC you get varies by payer. Pull 20 of your own 835s and confirm the pairings before your team hard-codes a workflow around them.

Patient Not Found Rejection vs a CARC 31 Denial

A patient not found rejection comes back on the 277CA before the payer adjudicates anything. A CARC 31 denial comes back on the 835 after adjudication. Your team fixes them two different ways.

On the rejection side, the clearinghouse or the payer’s front end fails the member lookup and returns a 277CA. The claim never reaches adjudication, so you get no 835, no denial, and no payer claim number to reference. Fix the identifiers and send it again the same day.

On the denial side, the claim got in. The payer searched its enrollment file, found nobody, and posted CAS 31 on the 835 with a claim number attached. Now you need the resubmission path in the next section, and the filing clock has been running since the date of service.

Portals label both events “patient not found,” which is where the confusion starts. Look at the transaction instead of the label, and our clearinghouse rejection codes guide maps the 277CA side in full. A 277CA means rejection. An 835 means denial.

One thing worth protecting: a rejected claim doesn’t hold your original submission date for timely filing. Resend it the day you see it.

Common Causes of PR-31 and CO-31 Denials

PR-31 denial code causes fall into seven buckets, and all seven are identifier problems. Your claim described a person the payer’s file can’t match.

• Typographical errors in the member ID: a transposed digit, a dropped alpha prefix or suffix, or last year’s number after the plan reissued cards. Your front desk touches this data at check-in, which is where an insurance eligibility verification services check confirms it before the claim leaves your system.
• Name mismatch: a nickname on the intake form, a missing middle initial, a two-part last name keyed in the wrong order, or a married name the payer never received. Payer systems match character by character.
• Wrong date of birth or sex: month and day reversed, or the subscriber’s birth date typed onto a dependent’s claim.
• Wrong payer or wrong plan: the claim went to a payer that never covered this patient, or to the wrong line of business inside a payer that did. When the payer recognizes the member and disputes the order instead, you get 22, and our CO-22 coordination of benefits guide covers that sequence. A Medicare Advantage or Medicaid managed care patient billed to the wrong program usually returns CO-24, which our CO-24 managed care denial guide walks through.
• Subscriber and dependent confusion: your system lists the patient as the subscriber when a parent or spouse holds the policy, a newborn hasn’t been added inside the plan’s window, or a dependent aged off mid-year.
• Coverage changes nobody captured: a new plan year, a January 1 Marketplace switch, an employer change, or a Medicaid MCO reassignment, with last year’s ID still sitting in the chart.
• Payer-side lag: the enrollment file wasn’t current when the claim adjudicated. Your data was right and the payer’s wasn’t. Run eligibility for the date of service, then ask for reprocessing rather than correcting data that was already correct.

MGMA’s January 6, 2026 poll named these same front-end failures: incorrect insurance entry, outdated demographics, retro terminations, and delays adding newborns. The numbers sit in the impact section below.

Where the Mismatch Lives: CMS-1500 Boxes and 837P Loops Behind Code 31

Code 31 traces back to six data elements: the insured’s ID, patient name, birth date and sex, insured’s name, patient relationship, and group number. They sit in CMS-1500 Items 1a, 2, 3, 4, 6, and 11 and in the 837P subscriber and patient loops.

One rule prevents most of it. Enter every element as printed on the card, and for Medicare, copy the Medicare card character for character, including the order of two last names. CMS publishes the item instructions in Chapter 26 of the Medicare Claims Processing Manual, and our CMS-1500 box-by-box guide translates them field by field.

Institutional billers work the same elements in different fields. On the UB-04 they sit in FL 58 through FL 62, covering the insured’s name, patient relationship, insured’s unique ID, group name, and group number, plus FL 8, 10, and 11 for the patient’s name, birth date, and sex.

How to Fix a PR-31 or CO-31 Denial

To fix a PR-31 denial code, confirm the identifiers against the card and a fresh eligibility response, correct the record and the claim, then resubmit on the path your payer requires. Appeals are the exception.

Six Steps That Clear Most 31s

1. Read the whole remittance line. Group code, CARC 31, any RARC, the CLP02 status, and the payer’s claim number.
2. Compare the identifiers character by character. Pull the card image and the intake form, then check the member ID with its prefix and suffix, legal name, birth date, sex, relationship, and group number.
3. Verify eligibility for the date of service. Run it through your clearinghouse 270/271, the payer portal, or the Noridian Medicare Portal for Medicare patients. When the 271 returns a member ID different from the one you sent, the ID changed, and that 271 becomes your proof.
4. Pick the path from the table below. New claim, replacement, reprocessing, or appeal.
5. Fix the patient record first, then the claim. Resubmit every open claim for that patient so the next one doesn’t deny for the same reason.
6. Watch the filing clock. A 31 doesn’t pause timely filing, which is where AR follow-up services earn their keep. Our CO-29 timely filing rules guide covers the deadline math by payer.

CO 31 Denial Code Solution by Payer Type: New Claim, Replacement, or Reprocessing

When nothing matches anywhere, stop resubmitting. Run coverage discovery, read the notes from prior dates of service, and call the patient for a current card. CO-31 is typically not appealed; it is corrected and resubmitted. Noridian’s DME reason code 31 guidance sets out the new-claim path for Medicare.

When 31s show up by the dozen, our claim denial management services separate the correctable ones from the true self-pay balances and work both, so nothing ages out.

How to Fix PR 31 Denials on the Phone: The Payer Call Script

1. Ask the rep to search by member ID, with and without the prefix or suffix.
2. Ask for a search by legal name, date of birth, and sex.
3. Ask for a search under the subscriber, meaning the spouse or parent, to surface a dependent.
4. Ask which field failed, whether they want a new claim or a replacement, and the filing limit from the date of service.
5. Record the call reference number and the rep’s name in the claim notes.

When the rep can’t find your patient by any path, you’re looking at a coverage question, and the patient is your next call.

PR-31 on Medicare Claims: MBI, Part B Entitlement, and the CO-16 Trap

On Medicare claims, the PR-31 denial code means the MAC couldn’t match the MBI and name on your claim to a beneficiary entitled to Part B on the date of service. The fix is a corrected new claim.

What Noridian Tells You to Check First

Noridian’s Part B guidance on reason code 31 sets out three checks.

1. Confirm Part B entitlement covers the date of service.
2. Match the MBI and the first and last name to the current Medicare card, in the printed order, including every character of a hyphenated or two-part last name.
3. Correct the claim and resubmit as a new claim.

When your identifiers are right and Medicare’s record is wrong, your billing team can’t fix it from this side. The patient corrects the record with Social Security at 800-772-1213, and a new card follows. Hold the claim with a dated note. Medicare’s filing limit runs 12 months from the date of service.

CO-16 With N382 vs PR-31: Two Different Medicare Messages

An MBI that fails format or lookup comes back as CO-16 with remark codes N382 and N704, which means unprocessable, resubmit, no appeal, per Noridian’s denial code resolution table. A valid MBI for a person without Part B entitlement comes back as PR-31.

Since CMS Transmittal R4047CP, MACs use N382 for a missing or invalid patient identifier and pair it with CO-16. When the name or personal characteristics don’t line up with the MBI, the Common Working File returns CO-16 with MA27 or N382. Medicare saves PR-31 for the case where it found no entitled beneficiary at all.

An MBI runs 11 characters, numbers and uppercase letters only, and CMS leaves out S, L, O, I, B, and Z. MBIs change, so a card from three years ago may be stale. Your team has three ways to get the current one: ask the patient, use your MAC’s lookup tool, or read it off the remittance advice.

Medicare Reason Code 31 Checklist

• Verify entitlement for the date of service in the MAC portal.
• Copy the MBI and name from the current red, white, and blue card rather than an old chart.
• Bill the plan when the patient carries a Medicare Advantage card. Original Medicare won’t claim the encounter.
• Route Railroad Retirement Board beneficiaries to the RRB Specialty MAC, Palmetto GBA, instead of your regional MAC.
• Expect CO-109 when the claim went to the wrong MAC jurisdiction, and our CO-109 wrong payer denial guide covers the reroute.

Can You Bill the Patient for a PR-31 or CO-31?

You can bill the patient for a PR-31 only after an eligibility check confirms the patient had no coverage with that payer on the date of service. A CO-31 is never billed to the patient.

PR is the group code for Patient Responsibility, and the payer used it because it found no member to hold liable. That doesn’t prove your patient was uninsured. It proves the payer couldn’t find them. Send a statement on a claim that was wrong, and you’ll handle a complaint, a refund, and a second denial.

1. Document the no-coverage finding with a 271 response or a dated portal screenshot for the date of service.
2. Ask the patient about other coverage and run coverage discovery before anyone calls the balance self-pay.
3. Bill the new payer when a current card turns up, and note the filing limit from the original date of service.
4. Move the balance to self-pay under your financial policy when nothing turns up.

For original Medicare, treat a co-31 denial code balance as unbillable and a PR-31 as billable only once you’ve confirmed entitlement was absent. Billing a beneficiary for amounts outside PR carries penalty exposure.

Chasing an updated card is phone work. A patient help desk handles those calls without pulling billers off the denial queue.

How to Prevent PR-31 and CO-31 Denials at the Front Desk

Preventing PR-31 denials takes three verification passes: at scheduling, 48 to 72 hours before the visit, and at check-in, with the card image captured each time.

• Scan the insurance card at every visit, both sides. Keying from memory or from last year’s chart is where transposed digits start.
• Run real-time eligibility twice. Once 48 to 72 hours out, then again at check-in, and adopt the member ID and name the 271 returns, because the payer’s version wins. Medicare teams query entitlement through CMS HETS 270/271.
• Build registration edits that block bad claims. Legal name as printed, birth date in the payer’s format, subscriber relationships, group number, and a rule that stops any claim marked “self” where the relationship field says child or spouse.
• Run a plan-year protocol. Re-verify every patient on the first visit after January 1, and any Medicaid patient after an MCO reassignment notice, because that’s when last year’s ID goes out on a new claim.
• Hold claims for newborns and new dependents. Wait until the dependent shows on the 271 or the plan’s add window closes.
• Handle Medicare on its own track. MBI from the current card or the MAC lookup tool, Part B dates confirmed, and the Medicare Advantage card checked before anything goes to original Medicare.
• Trend the code monthly by payer, provider, and location. A 31 spike after a system migration, a new front-desk hire, or a payer merger points at a workflow break.

Our eligibility verification workflow guide covers the timing and scope step by step. A 31 is the cheapest denial to prevent and one of the most expensive to leave alone, because it repeats on every claim you file for that patient until someone corrects the record.

If your front desk can’t reach a second verification pass before the visit, our outsourced eligibility verification runs it 48 to 72 hours out, validates demographics and coordination of benefits, and posts the results into your EHR.

Codes Often Confused With 31: 26, 27, 32, 140, 22, 109, 16, 24, and 224

Code 31 means the payer never found the member. The codes below mean the payer found the member and denied for a different reason, which is why each one takes a different fix. Column two carries the official X12 wording.

X12 deactivated CARC 28, “Coverage not in effect at the time the service was provided,” on October 16, 2003 as redundant to 26 and 27. When a payer still sends it, work it as a 26 or a 27.

Guides for 27, 22, 16, 24, and 109 sit linked in the sections above. This table stays link-free so your team can quote a row without chasing anything.

What Changed in 2026 for Code 31, and What Didn’t

Denial code 31 has carried the same wording since September 30, 2007. The code list around it moved in 2026, along with the Medicare systems that load that list and a federal rule governing how plans report these codes.

• X12 list status. The CARC list X12 posts is the November 1, 2025 version, marked Status Last Reviewed on August 1, 2026, and X12 publishes code updates around March 1, July 1, and November 1 each year. Your ERA mapping table has to move on that same cadence.
• CMS Transmittal 13666, Change Request 14410. CMS issued it March 25, 2026, with an effective date of July 1, 2026 and an implementation date of July 6, 2026. It directs the Medicare shared systems to load the July 2026 CARC and RARC lists and update MREP and PC Print. A remit read through last year’s table can mislabel a code.
• No Surprises Act remittance codes. The Departments published the Federal IDR Operations final rules on June 4, 2026, and CMS followed with guidance on July 17, 2026 covering the remark codes plans must use on remittances to non-contracted providers in those situations. For out-of-network practices, the group code and remark code on a 31 now carry more weight in deciding whether you can bill the balance at all.

Old code, current problem. Confirm your billing system refreshed its CARC and RARC tables after July 6, 2026, and re-read any 31 that arrived with a remark code your team doesn’t recognize before routing it. This guide reflects the code list as of September 2026.

What a 31 Costs You: The 2026 Numbers

MGMA’s January 6, 2026 poll found denials and appeals to be the biggest revenue cycle leak for 48% of medical group leaders, with front-end issues second at 23%. The front-end failures those leaders named are the ones behind code 31.

MGMA listed them by name: incorrect insurance entry, outdated demographics, retro terminations, and delays adding newborns. The rest of the poll split across billing and collections at 14%, coding at 13%, and charge posting at 2%. The poll drew 288 applicable responses.

Medicare adds its own pressure. CMS reported a 6.55% improper payment rate for Medicare fee-for-service in fiscal year 2025, totaling $28.83 billion, with Part B providers at 8.44%. A payment made on a misidentified beneficiary counts as improper, which explains why MACs match identifiers to the letter.

Your own number beats any of these. Count last quarter’s 31s, multiply by your average charge, add the hours your team spent reworking them, and you’re looking at the prevention budget.

PR-31 and CO-31 Denial Code FAQs

What does denial code PR-31 mean?

Denial code PR 31 means the payer cannot identify the patient as its insured, and the balance sits in patient responsibility until someone corrects the claim. It’s CARC 31 carrying the PR group code, written by some systems as PR31 or denial code PR31. An identifier mismatch or a claim sent to the wrong payer causes most of them. Correct the member ID, name, birth date, or subscriber data, then resubmit. Payer wording for pr 31 denial code descriptions varies, so read the remark code beside it.

What is a CO-31 denial?

A CO-31 denial is the same reason code 31 posted with the Contractual Obligation group code, so the unpaid amount stays with the provider and can’t be billed to the patient. Some commercial payers and state Medicaid crosswalks use CO where Medicare uses PR. The CO 31 denial code descriptions on the EOB read the same as PR-31, so your posting team checks the group code before generating a statement. Watch for the mistyped forms too, including CO31 denial code and C0 31.

What does the 31 remark code mean?

There is no remark code 31. The number 31 belongs to the reason code list, and the remark codes that ride with it are N382, MA27, MA36, MA61, MA130, and N704. N31 and MA31 are unrelated remark codes covering a prescribing provider identifier and a billing period. Read the RARC column on your 835 to find the field that failed, because CARC 31 alone tells you the category and the RARC tells you the fix.

What is reason code 31?

Reason code 31 is Claim Adjustment Reason Code 31 on the X12 list, active since January 1, 1995 and last modified September 30, 2007, meaning “Patient cannot be identified as our insured.” It reaches you as PR-31 or CO-31 depending on the group code the payer attaches. Medicare Administrative Contractors post it as PR-31. X12 maintains the list and publishes updates around March 1, July 1, and November 1 each year.

What is the difference between a rejection and a denial for patient not found?

A patient not found denial code on the 835, meaning CARC 31, tells you the payer adjudicated your claim and denied it. A patient not found rejection on the 277CA tells you the claim never got into the payer’s system. Resend a rejection the same day with corrected identifiers. Work a denial through the new-claim or replacement path your payer requires. The filing clock runs from the date of service in both cases, so neither one buys you time.

Can you appeal a PR-31 denial?

Usually not. A PR-31 gets corrected and resubmitted, and Medicare’s MACs direct you to send a new claim rather than an appeal. Appeal it when the payer insists the member doesn’t exist and your 271 eligibility response proves otherwise. Attach that 271, the card image, and the original claim details to the appeal. Sending an appeal for your own data error delays payment by weeks while timely filing keeps running.

What does code 31 mean on a health insurance claim?

On a remittance, code 31 is the reason code for patient cannot be identified as our insured. Claim forms use 31 for something else: place of service 31, a skilled nursing facility, which has no connection to the denial. Check where the 31 sits. Inside the CAS segment on an 835, it’s a denial. In the place-of-service field, it’s a facility code, and our POS 31 place of service guide covers that one.

Is PR-31 a soft denial or a hard denial?

A PR-31 denial code is a soft denial. Your team can correct the underlying data and clear it on resubmission without a formal appeal. It hardens into a write-off when it ages past the payer’s filing limit, which is the real risk with this code. Practices that work 31s inside five business days of the remittance date rarely lose one to timely filing.

What to Do With Your Next PR-31

A PR-31 denial code points at a failed lookup. Correct the identifiers, pick the resubmission path your payer requires, and keep the filing clock in view. The group code tells you who’s waiting on the money.

If PR-31 shows up as a recurring line on your aging report, our denial management team can work the backlog while your front desk fixes the intake step producing it. One O Seven RCM handles eligibility through final payment for practices in all 50 states.