Claim adjustment reason code · X12

CO-15: authorization number missing or invalid.

CARC 15 said the authorization number was missing, invalid, or did not apply to the billed services or provider. X12 gives it a stop date of 05/01/2018. If you see it, the problem is still the authorization on the claim: find the real number, match it to the service and provider, and correct the claim.

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What X12 says CARC 15 means

The authorization number is missing, invalid, or does not apply to the billed services or provider.

CARC 15 · Start 01/01/1995, last modified 11/01/2017, stopped 05/01/2018 (retired).

In plain terms: X12 retired this code on 05/01/2018. When a payer still shows it, it means the authorization number was missing, wrong or did not match the service or provider.

What it means on a remittance

The X12 list marks CARC 15 as stopped on 05/01/2018, so a current X12 code list no longer treats it as an active code. It still turns up in old remittances, billing-system histories and search results, which is why it is explained here. For the same problem today, look at CARC 197 (precertification, authorization, notification or pre-treatment absent) and the remark codes M62 and N54, which speak to the authorization number and to a mismatch with what was authorized.

Typical causes

The authorization number was left off the claim or keyed with a digit wrong.
The number belongs to a different service, date range, unit count or facility than the one billed.
The authorization was issued to a different rendering or billing provider.
The authorization had expired, or the visit fell outside its approved dates.

These are common billing patterns, not a diagnosis of your claim. The remittance and the payer's policy decide.

What to check

Pull the authorization record from the payer portal or the approval letter and write down the number, approved codes, units, dates and provider.
Compare each item with the denied line. Confirm the provider with the NPI lookup.
Check that the number sits in the field the payer's claim format expects. The payer's companion guide says which.
If no authorization exists, see CARC 197 for the absent-authorization path.

Correct, resubmit or appeal

If the number was wrong or missing, submit a corrected claim with the right one. If the authorization exists and matches but the payer denied anyway, ask for review: for Medicare, redetermination within 120 days of receipt of the notice, with receipt presumed 5 days after the notice date. For other payers, the plan's own appeal window applies.

Medicare dates that apply

Medicare claims must be filed no later than the close of the period ending 1 calendar year after the date of service (42 CFR 424.44(a)(1)), with exceptions in 424.44(b). A redetermination request must be filed within 120 calendar days from the date a party receives the notice, receipt is presumed 5 days after the notice date (42 CFR 405.942(a)), and a late request can be considered for good cause (405.942(b)). Clerical errors, including inaccurate data entry, are handled by the contractor as reopenings instead of redeterminations (42 CFR 405.980(a)(3)). The tool above runs the date math.

Related codes

X12 does not publish a table that pairs each CARC with remark codes; the payer picks the remark code and prints it beside the CARC on the same remittance line. These X12 remark codes carry wording that speaks to this reason, so look for them:

M62 — Missing/incomplete/invalid treatment authorization code.
N54 — Claim information is inconsistent with pre-certified/authorized services.

Other codes: CARC 197 (authorization absent), CARC 16 (missing or wrong claim data). The full lookup reads any code on this page.

Worked example (hypothetical)

A therapy visit denies with an authorization-number message. The approval letter shows 12 visits ending on March 31, and the claim was keyed with a number from an earlier episode. The biller enters the new number, resubmits, and notes the correction date.

Sources

X12: Claim Adjustment Reason Codes — code text, usage notes and dates (list dated 10/30/2026, retrieved 2026-11-02)
X12: Remittance Advice Remark Codes — remark code text (retrieved 2026-11-02)
42 CFR 424.44, 42 CFR 405.942 and 42 CFR 405.980 — eCFR, current through 2026-10-29 (retrieved 2026-11-02)

Code descriptions are X12 copyrighted material, quoted here only for the codes on this page and linked to the owner. For the full lists, use X12. Every rule above was read from these pages on November 2, 2026. Payers revise code lists, contracts and policies, so confirm anything that affects a claim or a deadline with the payer.

Frequently asked questions

Is CARC 15 still in use?

The X12 list shows a stop date of 05/01/2018 for CARC 15. Payers may still describe the same problem in other terms, so match your remittance against the code list on the day you read it.

What replaced CARC 15?

X12 does not name a single replacement in its entry for CARC 15. CARC 197 covers an absent authorization, and the remark codes M62 and N54 speak to the authorization number and to a mismatch with the authorized services.

Do I appeal or correct the claim?

If the number was wrong, correct and resubmit. If the number was right and the payer disagrees, appeal under the payer's rules. For Medicare the redetermination window is 120 days from receipt of the notice.

Not legal, billing or medical advice

This page explains published code lists and rules and runs a lookup in your browser. It cannot see your claim, your contract or any payer's policy. Confirm with the payer or your Medicare Administrative Contractor before you resubmit, appeal or bill a patient.