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 |
|---|---|---|
| M22 | Missing/incomplete/invalid number of miles traveled. | Details → |
| M23 | Missing invoice. | Details → |
| M23 | Missing invoice. | Details → |
| M24 | Missing/incomplete/invalid number of doses per vial. | Details → |
| M24 | Missing/incomplete/invalid number of doses per vial. | Details → |
| M25 | The information furnished does not substantiate the need for this level of service. I… | Details → |
| M25 | The information furnished does not substantiate the need for this level of service. I… | Details → |
| M26 | The information furnished does not substantiate the need for this level of service. I… | Details → |
| M26 | The information furnished does not substantiate the need for this level of service. I… | Details → |
| M27 | Alert: The patient has been relieved of liability of payment of these items and servi… | Details → |
| M27 | Alert: The patient has been relieved of liability of payment of these items and servi… | Details → |
| M28 | This does not qualify for payment under Part B when Part A coverage is exhausted or n… | Details → |
| M28 | This does not qualify for payment under Part B when Part A coverage is exhausted or n… | Details → |
| M29 | Missing operative note/report. | Details → |
| M29 | Missing operative note/report. | Details → |
| M3 | Equipment is the same or similar to equipment already being used. | Details → |
| M3 | Equipment is the same or similar to equipment already being used. | Details → |
| M3 | Item billed is same or similar to an item already received in beneficiary's history | Details → |
| M30 | Missing pathology report. | Details → |
| M30 | Missing pathology report. | Details → |
| M31 | Missing radiology report. | Details → |
| M31 | Missing radiology report. | Details → |
| M32 | Alert: This is a conditional payment made pending a decision on this service by the p… | Details → |
| M32 | Alert: This is a conditional payment made pending a decision on this service by the p… | Details → |
| M33 | Missing/incomplete/invalid UPIN for the ordering/referring/performing provider. | Details → |
| M33 | Missing/incomplete/invalid UPIN for the ordering/referring/performing provider. | Details → |
| M34 | Claim lacks the CLIA certification number. | Details → |
| M34 | Claim lacks the CLIA certification number. | Details → |
| M35 | Missing/incomplete/invalid pre-operative photos or visual field results. | Details → |
| M35 | Missing/incomplete/invalid pre-operative photos or visual field results. | Details → |
| M36 | This is the 11th rental month. We cannot pay for this until you indicate that the pat… | Details → |
| M36 | This is the 11th rental month. We cannot pay for this until you indicate that the pat… | Details → |
| M37 | Not covered when the patient is under age 35. | Details → |
| M37 | Not covered when the patient is under age 35. | Details → |
| M38 | Alert: The patient is liable for the charges for this service as they were informed i… | Details → |
| M38 | Alert: The patient is liable for the charges for this service as they were informed i… | Details → |
| M39 | Alert: The patient is not liable for payment of this service as the advance notice of… | Details → |
| M39 | Alert: The patient is not liable for payment of this service as the advance notice of… | Details → |
| M4 | Alert: This is the last monthly installment payment for this durable medical equipmen… | Details → |
| M4 | Alert: This is the last monthly installment payment for this durable medical equipmen… | Details → |
| M40 | Claim must be assigned and must be filed by the practitioner's employer. | Details → |
| M40 | Claim must be assigned and must be filed by the practitioner's employer. | Details → |
| M41 | We do not pay for this as the patient has no legal obligation to pay for this. | Details → |
| M41 | We do not pay for this as the patient has no legal obligation to pay for this. | Details → |
| M42 | The medical necessity form must be personally signed by the attending physician. | Details → |
| M42 | The medical necessity form must be personally signed by the attending physician. | Details → |
| M43 | Payment for this service previously issued to you or another provider by another carr… | Details → |
| M43 | Payment for this service previously issued to you or another provider by another carr… | Details → |
| M44 | Missing/incomplete/invalid condition code. | Details → |
| M44 | Missing/incomplete/invalid condition code. | Details → |
| M45 | Missing/incomplete/invalid occurrence code(s). | Details → |
| M45 | Missing/incomplete/invalid occurrence code(s). | Details → |
| M46 | Missing/incomplete/invalid occurrence span code(s). | Details → |
| M46 | Missing/incomplete/invalid occurrence span code(s). | Details → |
| M47 | Missing/incomplete/invalid Payer Claim Control Number. Other terms exist for this ele… | Details → |
| M47 | Missing/incomplete/invalid Payer Claim Control Number. Other terms exist for this ele… | Details → |
| M48 | Payment for services furnished to hospital inpatients (other than professional servic… | Details → |
| M48 | Payment for services furnished to hospital inpatients (other than professional servic… | Details → |
| M49 | Missing/incomplete/invalid value code(s) or amount(s). | Details → |
| M49 | Missing/incomplete/invalid value code(s) or amount(s). | 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.