guide

Prior authorization denial codes: what they mean and how to act

CO-15, CO-197, PR-242, CO-107, and more (this guide decodes the CARC and RARC systems behind prior authorization denial codes and delivers sequenced response).
Jeffrey Morelli
Jeffrey Morelli
Published 21 June 2026

A prior authorization denial is not one problem; it is a family of problems, and the code on the remittance tells you which one you have. The most common codes look almost identical on the page yet demand entirely different responses on entirely different clocks. Reading the code correctly is the difference between a same-day fix and a forfeited appeal.

This guide is written for billers and authorization coordinators who work prior authorization denials at volume. It decodes the CARC and RARC systems that appear on every remittance, names the verified codes that signal an authorization problem, and lays out a response protocol so no denial sits unworked past its deadline.

How CARC and RARC codes work

Every ERA (the EDI 835 transaction) and every paper EOB carries at least two code types working together. The Claim Adjustment Reason Code (CARC) states why a payment was reduced or denied. The Remittance Advice Remark Code (RARC), the N-prefixed codes, adds specificity to that reason and frequently names the precise element that is missing or out of order. A biller who reads only the CARC sees that authorization failed; the RARC often says exactly how it failed, and that distinction changes what you submit in response. Always read the RARC text on the remittance rather than assuming what a given remark number means.

Both code lists are maintained by X12 and updated on a rolling cycle, so a description can shift between releases. Verify any code against the current official X12 CARC/RARC external code list before you act on it; this guide reflects the published meanings but should not substitute for the live list.

Every CARC is prefixed by a Claim Adjustment Group Code that identifies who absorbs the adjustment:

Group Code Full Name Who Absorbs the Adjustment Example Scenario
CO Contractual Obligation Provider absorbs; cannot bill patient Auth not obtained before service
PR Patient Responsibility Patient owes the balance Out-of-network service, deductible
OA Other Adjustment Neither party; administrative offset Coordination of benefits adjustment
PI Payer Initiated Payer adjusts without provider error Payer data correction

When an authorization denial carries the CO prefix, the provider absorbs the loss unless the denial is corrected or successfully appealed. That financial consequence is why a CO-prefixed authorization code has to be worked fast and worked correctly.

The prior authorization denial codes billers see most

The five Claim Adjustment Reason Codes below are the ones that signal an authorization problem on a remittance. Each pairs with a group code (most often CO) and an explanatory RARC. Confirm every code against the current X12 CARC list before acting, because descriptions are revised on rolling cycles.

CARC Plain-Language Meaning Most Common Cause Immediate Action
197 Precertification/authorization/notification/pre-treatment absent Authorization never requested before the service date Retroactive authorization request, or appeal with clinical notes
15 The authorization number is missing, invalid, or does not apply to the billed services or provider Wrong, expired, or inapplicable auth number on the claim Correct or confirm the auth number and resubmit; often no formal appeal
198 Precertification/authorization/notification/pre-treatment exceeded Service ran past the authorized units, visits, or date range Request additional units or an extension, or appeal with justification
252 An attachment/other documentation is required to adjudicate this claim/service Records not supplied at submission Submit the requested records inside the payer’s development window
39 Services denied at the time authorization/pre-certification was requested Authorization was sought but the payer declined it Review the denial rationale; appeal with clinical support if medically necessary

CARC 197 is the most consequential code on this list. It means no authorization existed at all, the service has already been rendered, and the appeal window is running.

197 vs 15 vs 198: the distinction billers get wrong

CARC 197, 15, and 198 all describe an authorization that did not hold up, and on a busy remittance they blur together. They are three different failures with three different fixes, and running the wrong workflow on any of them costs days you cannot get back.

CARC 197 means no authorization was obtained. There is nothing on file with the payer. The service was delivered without the required precertification, so the only paths are a retroactive authorization request, where the plan allows one, or a formal appeal arguing medical necessity with clinical notes. This is the heaviest of the three to resolve because there is no prior decision to point back to.

CARC 15 means an authorization existed but the number on the claim is wrong or does not apply. The number is missing, mistyped, expired, or attached to a different service or rendering provider than the one billed. The usual fix is administrative: confirm the valid authorization, correct the number, and resubmit. A formal appeal is frequently unnecessary because the authorization itself was good; only the claim data was off.

CARC 198 means a valid authorization was in place but the claim went beyond it. The payer approved a set number of units, visits, or a specific date range, and the billed service exceeded that limit. The response is to request additional units or an extension, or to appeal with justification for why the additional service was medically necessary.

The practical test: ask whether an authorization exists, and if so whether the problem is its identity or its limits. No authorization at all is 197. A bad or inapplicable authorization number is 15. A good authorization that the service outgrew is 198. Read the accompanying RARC for the exact element at issue, and verify the timely-filing or development deadline in the payer’s provider manual before you start, because those windows vary by payer.

A response protocol for each denial type

Authorization denials require sequenced responses, and the right sequence depends on the code. The protocols below cover the five verified codes.

For CARC 197 (authorization absent):

  1. Confirm the service actually required prior authorization under the patient’s benefit plan.
  2. If it did and none was obtained, submit a retroactive authorization request immediately, with clinical notes supporting medical necessity.
  3. If the payer denies the retroactive request, file a formal appeal with full clinical documentation.
  4. Record the denial date and track the appeal window from it.

For CARC 15 (authorization number missing, invalid, or inapplicable):

  1. Pull the original authorization confirmation from the payer portal or fax record.
  2. Compare the authorization number, service, and rendering provider on the claim against the confirmed authorization on file.
  3. If the number was mistyped or omitted, correct it and resubmit; no formal appeal is required when the authorization itself was valid.
  4. If the authorization does not cover the billed service or provider, determine whether a corrected or additional authorization is needed before resubmitting.

For CARC 198 (authorization exceeded):

  1. Pull the authorization and confirm the approved units, visits, and date range.
  2. Identify exactly how the billed service exceeded that limit.
  3. Request additional units or an extension where the plan allows it, or file an appeal with clinical justification for the additional service.
  4. Flag near-limit authorizations in scheduling so future visits do not run past the approved scope.

For CARC 252 (documentation required):

  1. Read the accompanying RARC carefully; it specifies what the payer needs.
  2. Gather the requested records: operative notes, clinical justification, referring provider information.
  3. Submit through the payer’s designated channel inside the development window. CARC 252 is a development request, not a final denial, and missing the window converts it to one.

For CARC 39 (denied at the time authorization was requested):

  1. Read the denial rationale on the remittance and the accompanying RARC.
  2. Assess whether the service is medically necessary and supportable against the payer’s criteria.
  3. If it is, appeal with clinical evidence; a peer-to-peer review with the reviewing medical director, where offered, can resolve it without spending formal appeal rights.

How Silna reduces denials

Most authorization denials are preventable at the front end. CARC 197, 15, and 198 all trace to process failures that happen before the claim is filed: authorization never requested, the wrong authorization number captured, or a service scheduled past the approved units or date range. By the time any of these codes lands on a remittance, the service is already delivered and the provider already carries the financial risk.

Silna Health’s Care Readiness Platform automates the workflow end to end: benefits verification, authorization requests, form population, real-time error checking, and multi-channel submission across payer portals. Silna’s Predictive Document Intelligence flags missing or mismatched authorization data and documentation gaps before the claim leaves the practice, catching the conditions that generate 197, 15, and 252 denials before the payer ever adjudicates. By combining automation with built-in payor communication, Silna cuts pre-visit administrative work by 95%, per Silna Health, 2026.

Silna’s strongest adoption is among ABA therapy, physical therapy, and mental health practices, plus care management for older adults, the practice types where authorization volume is highest and where a single missed unit or expired window stalls care. For teams working denials across multiple payers, Silna coordinates the full workflow so the first submission is the complete submission and fewer claims come back with a CARC at all. See how it applies to your payer mix at silnahealth.com.

Key terms

CARC (Claim Adjustment Reason Code)
The X12-maintained code on a remittance that states why a payment was reduced or denied.
RARC (Remittance Advice Remark Code)
The N-prefixed companion code that adds specificity to a CARC, often naming the exact missing element or corrective step.
Group code (CO, PR, OA, PI)
The prefix that identifies who absorbs the adjustment; CO (Contractual Obligation) means the provider cannot bill the patient for it.
ERA / EDI 835
The Electronic Remittance Advice transaction that carries the CARC and RARC codes for each adjudicated claim.
Development request
A payer’s request for additional documentation (CARC 252) before a final decision; converts to a denial if unanswered in time.
Retroactive authorization
An authorization requested after the service was rendered, where the plan permits one; a primary path for resolving a CARC 197 denial.

Frequently Asked Questions

What is the difference between CARC 197 and CARC 15?

CARC 197 means precertification or authorization was absent: none was obtained before the service. CARC 15 means an authorization number was supplied but is missing, invalid, or does not apply to the billed service or provider. CARC 197 typically requires a retroactive authorization request or a formal appeal with clinical notes, while CARC 15 usually only requires correcting or confirming the authorization number and resubmitting, with no formal appeal needed.

What does CARC 198 mean on an authorization denial?

CARC 198 means precertification or authorization was exceeded: a valid authorization was in place, but the billed service went beyond the approved units, visits, or date range. Unlike CARC 197 (no authorization at all) or CARC 15 (a bad authorization number), the authorization here was good; the service simply outgrew it. The response is to request additional units or an extension, or to appeal with justification for why the additional service was medically necessary.

What happens if you do not respond to a CARC 252?

CARC 252 is a request for additional documentation to adjudicate the claim, not a final denial. The payer is asking for records before deciding. If the provider does not submit the requested documentation within the payer’s development window, the claim converts to a denial. Read the accompanying RARC, which specifies exactly what documentation the payer needs, and submit it through the designated channel before the window closes.

What does the CO group code prefix mean on an authorization denial?

CO stands for Contractual Obligation. It means the provider absorbs the adjustment and cannot bill the patient for the denied amount. On an authorization denial, that financial consequence stands unless the denial is corrected through resubmission or successfully overturned on appeal, which is why CO-prefixed authorization codes need to be worked quickly.

Should I trust a code description without checking the X12 list?

No. CARC and RARC codes are maintained by X12 and updated on rolling cycles, so a description can change between releases. Always verify the code against the current official X12 CARC/RARC external code list, and read the specific RARC text on your remittance rather than assuming a remark number’s meaning, because the RARC frequently names the exact missing element that determines your next action.

This article is general educational information, not medical or insurance advice. Coverage rules, claim adjustment codes, and clinical criteria vary by plan, payer, and state, so consult a licensed healthcare professional or your plan administrator about your specific situation.

About the author

Jeffrey Morelli

Jeffrey Morelli is the Co-Founder and CEO of Silna Health, the first Care Readiness Platform built to remove the administrative barriers that delay care. Silna automates benefit checks, eligibility, and prior authorizations across 1,000+ payors, and is backed by $27M from Accel and Bain Capital Ventures. Before Silna, Jeff spent a decade in San Francisco building and scaling products for highly regulated industries, including leading go-to-market at Truework (Series C, acquired by Checkr).

Last reviewed: June 25, 2026.