Denial Code 55 (CO-55, PR-55) — Meaning & What to Do
Claim Adjustment Reason Code (CARC)
What denial code 55 means: The service is considered experimental or investigational by the plan.
What to do about denial code 55: Ask your doctor whether an appeal with clinical evidence is worthwhile.
CO-55 vs PR-55 vs OA-55: what the prefix means
| Code on your EOB | What the prefix means | Who typically pays |
|---|---|---|
| CO-55 | Contractual obligation — the provider writes the amount off | Usually not the patient |
| PR-55 | Patient responsibility | The patient |
| OA-55 | Other adjustment | Often another payer or plan |
The prefix tells you who is expected to absorb the amount; the number (55) tells you why.
Seeing denial code 55 on your EOB?
A denial code tells you what the payer reported, but it may not tell the whole story. Reviewing your EOB and bill together can help clarify what may need attention.
Related codes
CARC 50The insurer decided this service was not medically necessary.
CARC 96This service is not covered by your plan.
CARC 45The charge was above the maximum allowed amount, and the excess was written off.
CARC 97This service is already included (bundled) in the payment for another service, so it isn't paid separately.
Keep reviewing your bill
- Medical Bill vs EOB: What Is the Difference?
- How to Dispute a Medical Bill — Find Billing Errors Before You Pay
- What Is an Itemized Medical Bill? How to Request One
Frequently asked questions about Denial code 55
What does denial code 55 mean on my EOB?
The service is considered experimental or investigational by the plan.
What should I do about denial code 55?
Ask your doctor whether an appeal with clinical evidence is worthwhile.
Seeing this code on your own EOB?
Upload the EOB, the bill, or both — MD Bill Check reads the codes on your documents, compares them side by side, and flags what's worth questioning. Free, no account needed.