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 |
|---|---|---|
| M76 | Missing/incomplete/invalid diagnosis or condition. | Details → |
| M76 | Claim/service lacks information or has submission/billing error(s) which is needed fo… | Details → |
| M76 | Missing/incomplete/invalid diagnosis or condition. | Details → |
| M77 | Missing/incomplete/invalid/inappropriate place of service. | Details → |
| M77 | The procedure code/bill type is inconsistent with the place of service Missing/incom… | Details → |
| M77 | Claim/service lacks information or has submission/billing error(s) Missing/incomplet… | Details → |
| M77 | Missing/incomplete/invalid/inappropriate place of service. | Details → |
| M78 | Missing/incomplete/invalid HCPCS modifier. | Details → |
| M78 | Missing/incomplete/invalid HCPCS modifier. | Details → |
| M79 | Missing/incomplete/invalid charge. | Details → |
| M79 | Missing/incomplete/invalid charge. | Details → |
| M8 | We do not accept blood gas tests results when the test was conducted by a medical sup… | Details → |
| M8 | We do not accept blood gas tests results when the test was conducted by a medical sup… | Details → |
| M80 | Not covered when performed during the same session/date as a previously processed ser… | Details → |
| M80 | HCPCS billed is included in payment/allowance for another service/procedure that was … | Details → |
| M80 | Not covered when performed during the same session/date as a previously processed ser… | Details → |
| M81 | You are required to code to the highest level of specificity. | Details → |
| M81 | You are required to code to the highest level of specificity. | Details → |
| M82 | Service is not covered when patient is under age 50. | Details → |
| M82 | Service is not covered when patient is under age 50. | Details → |
| M83 | Service is not covered unless the patient is classified as at high risk. | Details → |
| M83 | Service is not covered unless the patient is classified as at high risk. | Details → |
| M84 | Medical code sets used must be the codes in effect at the time of service. | Details → |
| M84 | Medical code sets used must be the codes in effect at the time of service. | Details → |
| M85 | Subjected to review of physician evaluation and management services. | Details → |
| M85 | Subjected to review of physician evaluation and management services. | Details → |
| M86 | Service denied because payment already made for same/similar procedure within set tim… | Details → |
| M86 | Item has met maximum limit for this time period. Payment already made for same/simila… | Details → |
| M86 | Service denied because payment already made for same/similar procedure within set tim… | Details → |
| M87 | Claim/service(s) subjected to CFO-CAP prepayment review. | Details → |
| M87 | Claim/service(s) subjected to CFO-CAP prepayment review. | Details → |
| M88 | We cannot pay for laboratory tests unless billed by the laboratory that did the work. | Details → |
| M88 | We cannot pay for laboratory tests unless billed by the laboratory that did the work. | Details → |
| M89 | Not covered more than once under age 40. | Details → |
| M89 | Not covered more than once under age 40. | Details → |
| M9 | Alert: This is the tenth rental month. You must offer the patient the choice of chang… | Details → |
| M9 | Alert: This is the tenth rental month. You must offer the patient the choice of chang… | Details → |
| M90 | Not covered more than once in a 12 month period. | Details → |
| M90 | Not covered more than once in a 12 month period. | Details → |
| M91 | Lab procedures with different CLIA certification numbers must be billed on separate c… | Details → |
| M91 | Lab procedures with different CLIA certification numbers must be billed on separate c… | Details → |
| M92 | Services subjected to review under the Home Health Medical Review Initiative. | Details → |
| M92 | Services subjected to review under the Home Health Medical Review Initiative. | Details → |
| M93 | Information supplied supports a break in therapy. A new capped rental period began wi… | Details → |
| M93 | Information supplied supports a break in therapy. A new capped rental period began wi… | Details → |
| M94 | Information supplied does not support a break in therapy. A new capped rental period … | Details → |
| M94 | Information supplied does not support a break in therapy. A new capped rental period … | Details → |
| M95 | Services subjected to Home Health Initiative medical review/cost report audit. | Details → |
| M95 | Services subjected to Home Health Initiative medical review/cost report audit. | Details → |
| M96 | The technical component of a service furnished to an inpatient may only be billed by … | Details → |
| M96 | The technical component of a service furnished to an inpatient may only be billed by … | Details → |
| M97 | Not paid to practitioner when provided to patient in this place of service. Payment i… | Details → |
| M97 | Not paid to practitioner when provided to patient in this place of service. Payment i… | Details → |
| M98 | Begin to report the Universal Product Number on claims for items of this type. We wil… | Details → |
| M98 | Begin to report the Universal Product Number on claims for items of this type. We wil… | Details → |
| M99 | Missing/incomplete/invalid Universal Product Number/Serial Number. | Details → |
| M99 | Missing/incomplete/invalid Universal Product Number/Serial Number. | Details → |
| MA01 | Alert: If you do not agree with what we approved for these services, you may appeal o… | Details → |
| MA01 | Alert: If you do not agree with what we approved for these services, you may appeal o… | Details → |
| MA02 | Alert: If you do not agree with this determination, you have the right to appeal. You… | 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.