Instantly find explanations, causes, and resolution steps for every Claim Adjustment Reason Code (CARC) and Remark Code.
Claim Adjustment Reason Codes (CARC) explain why a payment differs from what was billed. Every 835 ERA and EOB uses these standardized codes.
Search any code or keyword above. Each page includes the full description, common causes, resolution steps, and appeal guidance.
Each denial code page also links to a dedicated Remark Code page — optimized for providers searching for ERA remark code context.
Most denials are reversible. Our guides walk you through the correct steps to correct, resubmit, or formally appeal each denial type.
| Code | Description | View |
|---|---|---|
| A0 | Patient refund amount. Start: 01/01/1995 | Details → |
| A01 | APC discounting applied. | Details → |
| A02 | APC packaged service. | Details → |
| A03 | Qualifies for APC outlier. | Details → |
| A04 | Qualifies for outlier with discounting. | Details → |
| A05 | APC packaged, considered in outlier amount. | Details → |
| A06 | APC pass-through, considered in outlier amount. | Details → |
| A07 | Denied. Seventh diagnosis invalid per code editor. | Details → |
| A08 | Denied. Eighth diagnosis invalid per code editor. | Details → |
| A09 | Denied. Ninth diagnosis invalid per code editor. | Details → |
| A1 | Claim/Service denied. At least one Remark Code must be provided (may be comprised of … | Details → |
| A1 | Oxygen equipment has exceeded number of approved paid rentals | Details → |
| A10 | Denied. Diagnosis and patient age are in conflict per the code editor. | Details → |
| A11 | Denied. Diagnosis and patient gender are in conflict per code editor. | Details → |
| A12 | THIS EOB IS INTENTIONALLY LEFT UNUSED | Details → |
| A13 | Denied. Procedure is invalid per code editor. | Details → |
| A14 | Denied. Procedure and patient age conflict per code editor. | Details → |
| A15 | Denied. Procedure and patient gender conflict per code editor. | Details → |
| A16 | Denied. Noncovered service per code editor. | Details → |
| A17 | Denied. Condition code 21 (verification of denial) billed. | Details → |
| A18 | Denied. Condition code 20 (submitted for review) billed. | Details → |
| A19 | Denied. Defined as "questionable covered service" by code editor. | Details → |
| A2 | Contractual adjustment. Start: 01/01/1995 | Last Modified: 02/28/2007 | Stop: 01/01/… | Details → |
| A20 | Denied. Per code editor. Code indicates site of service not in Outpatient Prospective… | Details → |
| A21 | Denied. Service units outside of range allowed for procedure. For units consideratio… | Details → |
| A22 | Denied. Per code editor, multiple bilateral procedures were billed without modifier -… | Details → |
| A23 | Denied. Per code editor, specification of bilateral procedure is inappropriate. | Details → |
| A24 | Denied. Even with modifier, code editor won't allow this mutually exclusive or compon… | Details → |
| A25 | Denied. Per code editor, medical visit without modifier -25 not allowed with type "T"… | Details → |
| A27 | Denied. Per code editor, terminated bilateral procedure can't have more than 1 unit. | Details → |
| A28 | Denied. Per code editor, the implementation or associated procedure is not consistent… | Details → |
| A29 | Denied. CCI edit would allow this w/ proper modifier. | Details → |
| A3 | Medicare Secondary Payer liability met. Start: 01/01/1995 | Stop: 10/16/2003 | Details → |
| A30 | Denied. Per code editor, multiple medical visits billed for same day without conditio… | Details → |
| A31 | Denied. Per code editor, blood product for transfusion or blood product exchange not … | Details → |
| A32 | Denied. Per code editor, observation revenue code billed with non-observation HCPCS c… | Details → |
| A33 | Denied. Per code editor, service is not separately payable. | Details → |
| A34 | Denied. Per code editor one or more, modifier(s) is invalid. | Details → |
| A35 | Denied. Per code editor, revenue center requires HCPCS code. | Details → |
| A36 | Denied. Per code editor, revenue code is invalid. | Details → |
| A37 | Denied. Inpatient bill submitted without patient prior authorization (PA#) number. Co… | Details → |
| A38 | Denied. Per code editor partial hospitalization requirements are not met. | Details → |
| A4 | Medicare Claim PPS Capital Day Outlier Amount. Start: 01/01/1995 | Last Modified: 09… | Details → |
| A41 | Denied. Per code editor, service has not met the criteria for separate observation pa… | Details → |
| A42 | Denied. Per code editor, observation service cannot be billed unless type of bill is … | Details → |
| A43 | Proc code not authd. For assistance contact L&I Medical Director's Office at 360-902-… | Details → |
| A44 | Bill denied. Per code editor, CA modifier requires patient status code 20. | Details → |
| A45 | Bill denied. Per code editor, bill lacks required device code for one of the procedur… | Details → |
| A46 | Line denied. Per code editor, incorrect billing of blood and blood products. | Details → |
| A49 | Denied. Per code editor, trauma response critical care code billed without revenue co… | Details → |
| A5 | Medicare Claim PPS Capital Cost Outlier Amount. Start: 01/01/1995 | Details → |
| A51 | Line item denied. Bill lacks required cornea/procedure code. | Details → |
| A52 | Payment made at maximum units for submitting service. For consideration, submit adjus… | Details → |
| A53 | Biosimilar HCPCS reported without biosimilar modifier. | Details → |
| A6 | Prior hospitalization or 30 day transfer requirement not met. Start: 01/01/1995 | Details → |
| A7 | Presumptive Payment Adjustment Start: 01/01/1995 | Stop: 07/01/2015 | Details → |
| A8 | Ungroupable DRG. Start: 01/01/1995 | Last Modified: 09/30/2007 | Details → |
| A82 | Denied. Non-case rate APC not allowed for treatment of industrial injury or invalid H… | Details → |
| A86 | Denied. This APC ID is not allowed for treatment of industrial injuries. | Details → |
| A91 | Denied. Principal diagnosis code invalid per code editor. | Details → |
Medical claim denial codes — formally known as Claim Adjustment Reason Codes (CARC) — are standardized identifiers maintained by the X12 standards body and used across all Medicare, Medicaid, and commercial payer 835 electronic remittance transactions. When a claim is paid at a different amount than billed, at least one CARC code must accompany the remittance advice to indicate the specific reason for the adjustment.
The most frequently encountered codes include CO-16 (missing or invalid claim information), CO-45 (charges exceeding fee schedule), PR-1 (patient deductible), CO-29 (timely filing deadline exceeded), and CO-4 (procedure code inconsistent with modifier). Each represents a distinct, actionable reason that has a defined resolution pathway.