CO-167 Denial Code: Diagnosis Not Covered

The official definition

“This (these) diagnosis(es) is (are) not covered”

That is the verbatim definition of CARC 167 from the X12 Claim Adjustment Reason Code set, the standardized codes every insurer uses on EOBs and remittance advices. The letters in front of the number are the group code. CO: Contractual Obligation: an adjustment between the provider and the insurer. An in-network provider should not bill you for CO amounts.

What it means in plain English

The insurer says treatment for this particular condition is excluded from your coverage. The issue is not that the treatment was unnecessary but that the diagnosis itself falls outside the plan. Check this one carefully: mental health and substance-use exclusions can violate federal parity requirements, and a miscoded diagnosis can land a covered condition in an excluded category.

What to check on your EOB

• The diagnosis code on the claim: is it actually the right code for your condition?
• Your plan documents for the claimed exclusion.
• For mental health or substance-use care: whether the exclusion violates mental health parity requirements.
• Whether ACA essential health benefit mandates require coverage of this condition.

What to do next

1. If the diagnosis code is wrong, ask the provider to correct and resubmit.
2. If the exclusion looks improper (parity violations, ACA-mandated benefits), appeal on that basis.
3. If the diagnosis is correct and legitimately excluded, ask your provider whether a covered diagnosis more accurately describes your condition.

Who's responsible

You + provider. Most denials carry a clear owner. Knowing whether the fix belongs to you, your doctor, or the billing office is half the battle. If it's the provider's error, you should not be paying for it.

Want the fundamentals first? Start with how to read an EOB and the 7 most common billing errors. This page is general information about standardized denial codes, not legal or medical advice.