Claim adjustment reason code
Denial code CO-50 meaning
CARC 50, usually seen as CO-50: The payer decided the service was not medically necessary for this patient.
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- Reason code
- CARC 50
- Short name
- Not medically necessary
- Plain meaning
- The payer decided the service was not medically necessary for this patient.
- Group codes
- CO-50: Contractual obligation. The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it. PR-50: Patient responsibility. The patient, or a secondary payer, may owe the amount.
Plain-English summary written by Rivvi. X12 owns the CARC list and its exact wording, which is not reproduced here. Read it on the X12 CARC list (list dated November 1, 2025, checked October 23, 2026). This page does not decide how a claim is paid.
Common causes
- The diagnosis does not meet the payer's coverage policy for the service.
- The documentation does not show why the service was needed.
- For Medicare, an LCD or NCD limits the covered diagnoses.
What to check before resubmitting
- Read the payer's coverage policy, LCD or NCD for the code.
- Check that the diagnosis codes and pointers match the documentation.
- For Medicare, the patient can be billed only with a valid ABN on file (modifier GA).
Remark codes that often come with it
Related reason codes
Related pages
Questions
What does denial code CO-50 mean?
The payer decided the service was not medically necessary for this patient. This is Rivvi's plain-English summary of CARC 50. X12's exact wording is on x12.org.
How do I fix CO-50?
Read the payer's coverage policy, LCD or NCD for the code. Check that the diagnosis codes and pointers match the documentation. For Medicare, the patient can be billed only with a valid ABN on file (modifier GA).
Can I bill the patient for CO-50?
When it comes with group code PR, the patient or a secondary payer may owe the amount. When it comes with CO, the provider writes it off.
Which group codes come with CARC 50?
Most often CO (contractual obligation) or PR (patient responsibility). The group code, not the reason code, says who owes the amount.
What is the difference between a CARC and a RARC?
A claim adjustment reason code (CARC) says why a claim line was paid differently than billed. A remittance advice remark code (RARC) adds detail, such as which field is missing.