Skip to main content
Call
CARC 31 · CO-31

CARC 31 Denial: Patient cannot be identified as our insured — How to Fix and Appeal

Reviewed by QuickIntell RCM Editorial Team · Last reviewed

Updated

TL;DR

CARC 31 (X12 Patient cannot be identified as our insured). CARC 31 means the patient demographics on the claim (member ID, name, date of birth, or sex) do not match any active member in the payer's enrollment file.

Official X12 description

“Patient cannot be identified as our insured.”

Source: X12 Claim Adjustment Reason Codes. The X12 External Code Lists are the single authoritative source for every CARC descriptor — always verify against the current release before building a claim-scrub rule.

What CARC 31 actually means

CARC 31 means the patient demographics on the claim (member ID, name, date of birth, or sex) do not match any active member in the payer's enrollment file. Sometimes this is a true ID error (wrong digit on the member ID), sometimes a name mismatch (married name vs. maiden name), and sometimes the patient is genuinely not enrolled with this payer. The fix is to re-verify eligibility against a primary source and correct the demographics on the rebill.

Common root causes

  • Member ID transcribed incorrectly at registration (off by one digit, transposed characters).
  • Patient's name on file differs from the name the payer has (legal name vs. preferred name, maiden vs. married).
  • Patient gave the wrong insurance card (e.g., spouse's card, expired card).
  • Date of birth mismatch due to data-entry error or patient confusion about DOB format.

Prevention checklist

  • Scan the insurance card at registration rather than keying it in manually.
  • Confirm patient's legal name matches the insurance card at every visit.
  • Auto-validate member ID format against the payer's published ID schema (length, prefix, alphanumeric rules) before submission.
  • Run 270/271 eligibility at registration and read the response, don't just check a box.

Appeal strategy — step by step

Most CARC 31 denials clear faster with the right remediation than with a formal appeal. Work the steps in order and escalate only when a lower-effort path has been ruled out.

  1. 1Re-run eligibility against the payer using multiple identifiers (member ID, name, DOB, and SSN if allowed).
  2. 2Submit a corrected claim with the validated demographics — formal appeal is rarely needed.
  3. 3If the patient is truly not enrolled with this payer, collect the correct coverage and rebill the right payer within its timely-filing window.
Sample appeal-letter language for CARC 31
[Provider letterhead] Re: Appeal of CARC 31 — Claim #{claim_number} Member: {member_name} · Member ID: {member_id} Date(s) of Service: {dos} On {remittance_date} this claim was adjusted with CARC 31: "Patient cannot be identified as our insured." We respectfully request reconsideration. The X12 External Code List definition of CARC 31 does not apply to this claim for the following reasons: 1. [Cite the clinical / coding / policy fact that rebuts the adjustment] 2. [Cite the supporting documentation attached — op note, EOB, LCD/NCD citation, NCCI edit indicator, modifier rationale] 3. [Cite the payer's own policy where applicable] Attached: {list supporting documents} Please process payment under the member's benefits. If additional information is required, contact the billing office at {provider_phone} or {provider_email}. Sincerely, {billing_manager_name}, {credentials}

Edit the bracketed fields before sending. This template is a starting point; a payer-specific appeal form may still be required — check the provider portal first.

Payer-specific notes

Payer-specific behavior for CARC 31 publishes here as the QuickIntell anonymized denial ETL ingests sufficient volume. In the meantime, consult the payer directory for the relevant provider manual and appeal form.

How common is CARC 31?

Search demand rank
#30

Out of 306 seeded CARCs, ranked by combined US monthly search volume for "CARC 31", "CO-31 denial", and "denial code 31".

Platform frequency
Pending ETL

Platform frequency ranks publish once the anonymized denial-rate pipeline reaches the publication threshold (strategy §12 Phase 2).

How QuickRCM prevents CARC 31

QuickRCM catches the root causes above before the 837 leaves the clearinghouse:

  • Claim-scrub rules fire on every root cause listed above — the scrub references the same X12 CAS segment logic that drives the denial, so what the payer checks, QuickRCM checks first.
  • When a denial lands, QuickRCM routes it to the correct worker with the documentation bundle already attached (op note, LCD citation, modifier rationale, EOB, primary 835).
  • Appeal templates tuned to each CARC (including this one) pull the supporting facts from the claim and fill the bracketed fields automatically.
See QuickRCM →Book a demo

Frequently asked questions — CARC 31

What does CARC 31 mean?

CARC 31 is an X12 Claim Adjustment Reason Code. The official definition is: "Patient cannot be identified as our insured." In plain English, the payer is telling you cARC 31 means the patient demographics on the claim (member ID, name, date of birth, or sex) do not match any active member in the payer's enrollment file. Sometimes this is a true ID error (wrong digit on the member ID), sometimes a name mismatch (married name vs. maiden name), and sometimes the patient is genuinely not enrolled with this payer. The fix is to re-verify eligibility against a primary source and correct the demographics on the rebill.

How do I resolve a CARC 31 (CO-31) denial?

Start with the most common root cause: Member ID transcribed incorrectly at registration (off by one digit, transposed characters). First step: Re-run eligibility against the payer using multiple identifiers (member ID, name, DOB, and SSN if allowed). See the full remediation and appeal checklist on this page before filing a formal appeal.

Is CARC 31 patient responsibility?

No — CARC 31 is typically carried under CO (Contractual Obligation) or OA (Other Adjustment), which means it is the provider's responsibility, not the patient's. Do not bill the patient unless the 835 CAS group code is PR.

What does CARC 31 look like on an EOB or 835 remittance?

On the 835 ERA, CARC 31 appears in Loop 2110 CAS segment as "CAS*CO*31*{amount}". On a paper EOB the same code prints in the Adjustment/Denial Reason column with the X12 description: "Patient cannot be identified as our insured." — usually paired with one or more RARC remark codes in the same remittance line for additional context.

Which RARC is paired with CARC 31?

CARC 31 is commonly observed with RARC MA27, MA36, N382. The RARC narrows the reason — for example, pointing at a missing modifier, an LCD citation, or a specific policy. Fix the underlying CARC first; the RARC usually clears with the corrected claim.

Disclaimer

This page is operational reference for medical-billing professionals. It is not legal, clinical, or contractual advice. X12 code descriptors are maintained by the X12 External Code Lists; always verify against the current X12 release and the payer's own published policy before submitting or appealing a claim.