CO-39: denied at the time of authorization request.

What X12 says CARC 39 means

Services denied at the time authorization/pre-certification was requested.

CARC 39 · Start 01/01/1995.

In plain terms: The services were denied at the time authorization or pre-certification was requested.

What it means on a remittance

The payer already denied the authorization or pre-certification request for these services before the claim arrived, and the claim carries that result. It is different from CARC 197, whose X12 text is about authorization being absent, and from retired CARC 15, which was about an authorization number being invalid.

Typical causes

• An authorization request was submitted and the payer denied it.
• The payer found the service not covered or not medically necessary at the request stage.
• The service was delivered after the denial.
• The authorization was denied for a different service, facility or provider than the one billed.

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

What to check

1. Find the payer’s authorization denial letter and its appeal rights and deadline.
2. Compare the denied request with the service billed.
3. Check whether a peer-to-peer or reconsideration was offered.
4. Confirm what was told to the patient before the service.

Correct, resubmit or appeal

Appeal the authorization denial with clinical documentation if you disagree. Do not rely on resubmitting the claim alone. If the denial stands, follow your contract and policies for the patient account, and note any notice the patient was given.

Medicare dates that apply

A Medicare redetermination request must be filed within 120 calendar days from the date a party receives the notice of the initial determination; receipt is presumed 5 calendar days after the notice date unless there is evidence to the contrary (42 CFR 405.942(a)), and a late request can be considered for good cause (405.942(b)). Other payers set their own appeal windows in the contract or plan documents, so read the notice for the date. The tool above runs the date math.

Related codes

X12 does not publish a table that pairs each code with remark codes; the payer picks the remark code and prints it beside the CARC on the same remittance line.

X12 remark codes whose wording speaks to this reason:

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

Other codes: CARC 197 (authorization absent), CARC 50 (not medically necessary) and the full lookup.

Worked example (hypothetical)

An MRI claim denies with CO-39. The biller finds the payer’s denial letter for the pre-service request, gathers the physician’s notes and files the appeal that the letter describes.

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 405.942 — 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. The X12 text and the Medicare rule above were read from these pages on November 2, 2026. Causes, checks and examples are general billing practice written for this page, not X12 content. Payers revise code lists, contracts and policies, so confirm anything that affects a claim or a deadline with the payer.