Claim adjustment reason code
Denial code CO-56 meaning
CARC 56, usually seen as CO-56: The payer decided the service has not been proven effective.
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- Reason code
- CARC 56
- Short name
- Not proven effective
- Plain meaning
- The payer decided the service has not been proven effective.
- Group codes
- CO-56: Contractual obligation. The provider absorbs the amount under its contract or the payer's rules. Do not bill the patient for it.
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 payer's policy does not cover the service for this use.
What to check before resubmitting
- Read the payer's policy.
- Appeal with evidence for this use.
Related reason codes
Related pages
Questions
What does denial code CO-56 mean?
The payer decided the service has not been proven effective. This is Rivvi's plain-English summary of CARC 56. X12's exact wording is on x12.org.
How do I fix CO-56?
Read the payer's policy. Appeal with evidence for this use.
Can I bill the patient for CO-56?
With group code CO, no. CO means the provider absorbs the amount under its contract or the payer's rules.
Which group codes come with CARC 56?
Most often CO (contractual obligation). 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.