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 |
|---|---|---|
| M13 | Denied. 10th-25th diagnosis code denotes a non-industrial condition or is not suffici… | Details → |
| M13 | Only one initial visit is covered per specialty per medical group. | Details → |
| M130 | Missing invoice or statement certifying the actual cost of the lens, less discounts, … | Details → |
| M130 | Missing invoice or statement certifying the actual cost of the lens, less discounts, … | Details → |
| M131 | Missing physician financial relationship form. | Details → |
| M131 | Missing physician financial relationship form. | Details → |
| M132 | Missing pacemaker registration form. | Details → |
| M132 | Missing pacemaker registration form. | Details → |
| M133 | Claim did not identify who performed the purchased diagnostic test or the amount you … | Details → |
| M133 | Claim did not identify who performed the purchased diagnostic test or the amount you … | Details → |
| M134 | Performed by a facility/supplier in which the provider has a financial interest. | Details → |
| M134 | Performed by a facility/supplier in which the provider has a financial interest. | Details → |
| M135 | Missing/incomplete/invalid plan of treatment. | Details → |
| M135 | Missing/incomplete/invalid plan of treatment. | Details → |
| M136 | Missing/incomplete/invalid indication that the service was supervised or evaluated by… | Details → |
| M136 | Missing/incomplete/invalid indication that the service was supervised or evaluated by… | Details → |
| M137 | Part B coinsurance under a demonstration project or pilot program. | Details → |
| M137 | Part B coinsurance under a demonstration project or pilot program. | Details → |
| M138 | Patient identified as a demonstration participant but the patient was not enrolled in… | Details → |
| M138 | Patient identified as a demonstration participant but the patient was not enrolled in… | Details → |
| M139 | Denied services exceed the coverage limit for the demonstration. | Details → |
| M139 | Denied services exceed the coverage limit for the demonstration. | Details → |
| M14 | No separate payment for an injection administered during an office visit, and no paym… | Details → |
| M14 | Assistant surgeon (modifier -80, -81, -82) not payable when cosurgeon (modifier -62) … | Details → |
| M14 | No separate payment for an injection administered during an office visit, and no paym… | Details → |
| M140 | Service not covered until after the patient's 50th birthday, i.e., no coverage prior … | Details → |
| M140 | Service not covered until after the patient's 50th birthday, i.e., no coverage prior … | Details → |
| M141 | Missing physician certified plan of care. | Details → |
| M141 | Missing physician certified plan of care. | Details → |
| M142 | Missing American Diabetes Association Certificate of Recognition. | Details → |
| M142 | Missing American Diabetes Association Certificate of Recognition. | Details → |
| M143 | The provider must update license information with the payer. | Details → |
| M143 | The provider must update license information with the payer. | Details → |
| M144 | Pre-/post-operative care payment is included in the allowance for the surgery/procedu… | Details → |
| M144 | Pre-/post-operative care payment is included in the allowance for the surgery/procedu… | Details → |
| M15 | Separately billed services/tests have been bundled as they are considered components … | Details → |
| M15 | Denied. Radiological guidance must be used when performing this procedure. | Details → |
| M15 | Separately billed services/tests have been bundled as they are considered components … | Details → |
| M16 | Alert: Please see our web site, mailings, or bulletins for more details concerning th… | Details → |
| M16 | Adjudicated per instructions from the Pension Adjudicator | Details → |
| M16 | Alert: Please see our web site, mailings, or bulletins for more details concerning th… | Details → |
| M17 | Alert: Payment approved as you did not know, and could not reasonably have been expec… | Details → |
| M17 | Denied. Prior authorization required. Please fax an authorization request form WWW.LN… | Details → |
| M17 | Alert: Payment approved as you did not know, and could not reasonably have been expec… | Details → |
| M18 | Certain services may be approved for home use. Neither a hospital nor a Skilled Nursi… | Details → |
| M18 | Denied. Please submit the appropriate ICD Code set (ICD-9 or ICD-10) based on the dat… | Details → |
| M18 | Certain services may be approved for home use. Neither a hospital nor a Skilled Nursi… | Details → |
| M18 | Beneficiary was inpatient on date of service billed | Details → |
| M19 | Missing oxygen certification/re-certification. | Details → |
| M19 | Corrected to adjust the original bill submitted. | Details → |
| M19 | Missing oxygen certification/re-certification. | Details → |
| M2 | Not paid separately when the patient is an inpatient. | Details → |
| M2 | Not paid separately when the patient is an inpatient. | Details → |
| M2 | Beneficiary was inpatient on date of service billed | Details → |
| M20 | Missing/incomplete/invalid HCPCS. | Details → |
| M20 | Missing/incomplete/invalid HCPCS. | Details → |
| M20 | Procedure code was invalid on the date of service Missing/incomplete/invalid HCPCS | Details → |
| M21 | Missing/incomplete/invalid place of residence for this service/item provided in a hom… | Details → |
| M21 | Missing/incomplete/invalid place of residence for this service/item provided in a hom… | Details → |
| M22 | Missing/incomplete/invalid number of miles traveled. | 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.