CO-39: Services Denied at Pre-Certification

What Does CO-39 Mean?

CO-39 places the authorization failure squarely on the provider. The payer is saying the service required pre-certification, and the provider either did not obtain it, obtained authorization for a different service, or performed the service after the auth was denied. The financial loss falls on the provider, and the patient cannot be billed. However, CO-39 is one of the more appealable denial codes — strong clinical documentation can overturn the payer's medical necessity determination.

When CARC 39 appears on a remittance, the payer is telling you that the service was denied at the authorization or pre-certification stage. This is not a standard "missing auth" code — it specifically means the authorization process was initiated (or should have been) and the payer said no. The service was either performed without authorization, performed after the auth request was denied, or performed with an expired or mismatched authorization.

This denial differs from CARC 38 (which typically covers services performed without any authorization attempt). CARC 39 focuses on situations where the pre-certification process was engaged and the outcome was unfavorable. The most frequent scenario is a provider submitting a prior auth request that the payer denied based on medical necessity criteria, followed by the provider performing the service anyway and submitting a claim. Less commonly, it appears when the authorization was obtained for a different procedure or expired before the service was rendered.

Under CO, this is the provider's financial responsibility. Many CO-39 denials are appealable — if you have strong clinical documentation demonstrating medical necessity, including physician notes, test results, and relevant clinical guidelines, a well-constructed appeal can overturn the denial. The key is providing evidence that the payer's initial medical necessity determination was incorrect. For emergency or urgent situations, most payers have a retroactive authorization process with a 48-72 hour submission window that should be used before the denial is issued.

Common Causes

How to Resolve

Determine whether the authorization was missing, denied, or mismatched — then either appeal with clinical evidence, obtain retroactive auth, or write off the balance.

1. Check for existing authorization Verify whether a valid authorization exists that was not attached to the claim. If found, resubmit the claim with the correct authorization number.
2. Request retroactive auth for urgent services If the service was emergent or urgent, submit a retroactive authorization request within the payer's timeframe (usually 48-72 hours). Include clinical documentation demonstrating the urgency.
3. Appeal with medical necessity documentation Compile the patient's medical records, physician notes, lab results, imaging, and a letter of medical necessity. Reference applicable clinical guidelines or payer-specific coverage criteria in your appeal.
4. Post the write-off if appeal fails If all appeal levels are exhausted, write off the balance as a contractual adjustment. Track CO-39 write-offs by procedure and payer to identify patterns that need operational changes.

Common RARC Pairings

The RARC code tells you exactly what triggered the CO-39:

How to Prevent CO-39

• Build prior authorization verification into the scheduling workflow — no appointment should be confirmed for auth-required services without a valid authorization number on file
• Maintain a payer-specific auth requirement matrix and update it quarterly as payer policies change
• Use automated prior auth submission tools integrated with your EHR to catch auth requirements at the point of order entry
• Track authorization expiration dates and alert staff when an authorized service approaches its valid window
• For emergency services, establish a standing protocol for retroactive auth submission within 48-72 hours

General Prevention

• Implement a pre-authorization verification step in the scheduling workflow — before any service that requires auth, confirm a valid authorization number is on file
• Maintain a payer-specific authorization requirement matrix that identifies which procedures require pre-certification for each major payer
• Use automated prior authorization tools integrated with your EHR to submit auth requests at the point of order entry
• Track authorization expiration dates and alert scheduling staff when an authorized service has not been performed within the valid window
• For emergency services, establish a protocol for submitting retroactive authorization requests within the payer's required timeframe (typically 48-72 hours)
• Verify that the authorized procedure and diagnosis codes match the planned service before performing the procedure

Also Filed As

The same CARC 39 may appear with different Group Codes:

Related Denial Codes