Denial code playbook

The operational companion to CARC codes. For each scenario: what actually happened, whether to correct or appeal, and what to change upstream so it stops. How to use it: work your queue by CARC family, look up the scenario, take the action, and implement the prevention. The prevention column is the one that compounds. This is not the full code set. CARC and RARC codes and their definitions are copyrighted and licensed by X12; reproducing the complete lists requires a license from X12, so this page (and CARC codes and RARC codes) cover only the highest-volume scenarios a biller actually needs, not an exhaustive reference. For a code that isn’t here, look it up at the authoritative source, x12.org/codes, and apply the same fix-or-appeal logic as the nearest scenario in this table.

Eligibility

CARC / RARC	Root cause	Fix or appeal	Prevention
CO-26, expenses prior to coverage	Service before the effective date	Verify; rebill correct payer, or bill the patient if permitted	Run eligibility at scheduling and check-in
CO-27, coverage terminated	Coverage lapsed before service	Verify; find current coverage; rebill	Re-check at check-in, not just at booking
CO-31, patient not identified as insured	Wrong member ID, name mismatch, or missing alpha prefix	Correct and resubmit	Scan the card; verify against the 271
CO-32, not an eligible dependent	Relationship or dependent coverage issue	Verify; rebill or bill the patient	Capture relationship accurately at registration
CO-177, eligibility requirements not met	Plan-specific requirement	Verify with the payer	Read the 271 fully, not just “active”

Authorization

CARC / RARC	Root cause	Fix or appeal	Prevention
CO-197, authorization absent, auth exists	Obtained but never entered in the structured field	Corrected claim (freq. 7) with the auth number	Scrubber edit blocking submission when a CPT on the payer’s auth list has no auth number
CO-197, no auth obtained	Auth requirement missed at scheduling	Request retro-auth; else appeal on medical necessity	Per-payer auth-required list built into scheduling
CO-198, authorization exceeded	Units or visits beyond what was authorized	Request additional units; appeal	Track authorized units against delivered units
CO-15, auth invalid or doesn’t apply	Auth doesn’t match CPT, dates, provider, or facility	Verify and correct, or obtain a matching auth	Verify auth details against the planned service before the visit
N54, claim inconsistent with authorized services	Same	Same	Same

Coding and medical necessity

CARC / RARC	Root cause	Fix or appeal	Prevention
CO-11, diagnosis inconsistent with procedure	Code pairing doesn’t support the service	Review; correct if wrong, appeal with documentation if right	Scrubber code-pair edits; clinician education
CO-4, modifier missing or inconsistent	Required modifier absent	Correct and resubmit	Scrubber modifier edits by code
CO-50, not medically necessary	Coverage policy not met, or documentation insufficient	Appeal citing the payer’s own policy and the LCD/NCD	Know your MAC’s LCDs; document to the criteria
CO-97, bundled	NCCI edit; included in another service’s allowance	Verify the edit. Modifier 59 or an X-modifier only if clinically justified	Run NCCI edits pre-submission
CO-151, information doesn’t support this many services	Units or frequency	Appeal with documentation	Document units and time explicitly
CO-167, diagnosis not covered	Benefit or coverage policy	Verify; usually not appealable	Check coverage before scheduling elective services
M81, code to highest specificity	Unspecified ICD-10 code used	Correct to a specific code	Scrubber edit flagging unspecified codes

Modifier 59 and the X-modifiers are enforcement-visible. Using them to bypass an NCCI edit without a genuine clinical basis is a recognized unbundling pattern. Use them where the clinical circumstances justify them and document why. See Billing compliance basics.

Timely filing

CARC	Root cause	Fix or appeal	Prevention
CO-29, filing limit expired, was submitted timely	Payer lost it, or it bounced in a rejection loop	Appeal with the clearinghouse acceptance report	Weekly no-acceptance report; same-day rejection work
CO-29, genuinely late	Charge entry lag, or a held claim aged out	Check exceptions: retro eligibility, COB delay, retro-effective enrollment. Else write off with a root cause.	Same-day charge entry; internal deadline inside the contractual one

Coordination of benefits

CARC	Root cause	Fix or appeal	Prevention
CO-22, may be covered by another payer	Wrong payer billed first	Determine order; bill the primary	Ask about other coverage at every registration
OA-23, prior payer adjudication	Informational on secondary claims	Not a denial	—
N4, missing prior carrier EOB	Secondary claim submitted without primary remittance	Resubmit with the primary’s 835 detail	Automate primary-EOB attachment on secondary claims
MA04, secondary needs primary payment info	Same	Same	Same

Credentialing and enrollment

CARC	Root cause	Fix or appeal	Prevention
CO-8, procedure inconsistent with provider type	Taxonomy mismatch with enrollment	Correct the taxonomy; verify enrollment	Verify claim taxonomy matches enrolled taxonomy at go-live
CO-185, rendering provider not eligible	Not credentialed, or not linked to the group contract	Resolve with payer enrollment, then rebill	Don’t schedule insured patients before the effective date
CO-206, NPI missing or invalid	EDI enrollment incomplete, or wrong NPI on the claim	Verify EDI enrollment and claim data	Test one claim per payer before volume
CO-B7, not certified for this procedure on this date	Service date before the provider’s effective date	Pursue retro-effective date; else unbillable	Track effective dates in the credentialing grid
CO-109, not covered by this payer/contractor	Wrong payer or MAC	Rebill correctly	Verify payer ID mapping

Duplicates

CARC	Root cause	Fix	Prevention
CO-18, exact duplicate	You resubmitted an adjudicated claim as a new original	Use frequency code 7 referencing the original claim number	Train billers: adjudicated claims get corrected, not resubmitted
N522, duplicate crossover	Medicare crossover already sent it to the secondary	Don’t submit the secondary separately when crossover applies	Know which payers auto-crossover

Non-covered, usually not errors

CARC	Meaning	Action
CO/PR-96, non-covered charge	Read the RARC. Benefit design.	Patient responsibility with proper notice, or write off
PR-204, not covered under the plan	Benefit design	Patient responsibility
CO-253, sequestration	Statutory Medicare reduction	Write off

Train billers to recognize the non-errors. CO-45, PR-1/2/3, CO-253, CO-97, and CO-96 generate large volumes of wasted appeal effort in practices that treat every adjustment as a denial.

Information requests

CARC / RARC	Action
CO-252, attachment required	Submit the documentation via the payer’s required channel
CO-16 + a RARC	Read the RARC, it names the missing element
CO-226, provider information not provided	Respond; the clock may be running
MA130, incomplete/invalid, no appeal rights	Submit a new claim. Do not appeal.

The prevention priority list

If you fix things in order of value, this is the order:

Eligibility at scheduling and check-in, with the 271 saved
A scrubber edit blocking submission when an authorization is required and missing
Same-day rejection work, plus a weekly no-acceptance report
Taxonomy and enrollment data verified at every payer go-live
Effective-date discipline, no insured patients before a clinician’s effective date
Same-day charge entry
NCCI and modifier edits in the scrubber
Automated primary-EOB attachment on secondary claims

Items 1–5 prevent the majority of denials in most practices, and four of them are enrollment or front-desk controls rather than billing ones.

CPOM & Legal

Payers

Clearinghouses & Vendors

EDI & Code Sets

Banking & Payments

Glossary & Appendices

Eligibility

Authorization

Coding and medical necessity

Timely filing

Coordination of benefits

Credentialing and enrollment

Duplicates

Non-covered, usually not errors

Information requests

The prevention priority list

​Eligibility

​Authorization

​Coding and medical necessity

​Timely filing

​Coordination of benefits

​Credentialing and enrollment

​Duplicates

​Non-covered, usually not errors

​Information requests

​The prevention priority list

Eligibility

Authorization

Coding and medical necessity

Timely filing

Coordination of benefits

Credentialing and enrollment

Duplicates

Non-covered, usually not errors

Information requests

The prevention priority list