CARC Code 55
The procedure or treatment is deemed experimental or investigational by the payer.
What this denial means
When you see CARC code 55 on your Explanation of Benefits (EOB), it means your insurer has denied the claim with the following reason: the procedure or treatment is deemed experimental or investigational by the payer.
This code is one of the most common denial reasons in the CARC system and appears across both employer-sponsored and ACA marketplace plans. How you respond depends on whether the denial is a patient-side or provider-side issue.
Can you appeal this?
Yes — this denial is patient-appealable. Cite peer-reviewed literature, FDA approval or clearance status, and relevant clinical practice guidelines establishing the treatment as standard of care for the diagnosis. Request the specific criteria relied on to classify the treatment as experimental and the reviewer credentials. External review is particularly effective for experimental/investigational denials under ACA-compliant plans.
Applicable federal regulations:
ERISA plans (employer-sponsored)
- ERISA § 503
- 29 CFR § 2560.503-1(h)
ACA plans (marketplace / individual)
- PHS Act § 2719
- 45 CFR § 147.136(b)
- 45 CFR § 147.136(c)
- 45 CFR § 147.136(d)
Your insurer's legal team is bound by these regulations. An appeal letter that cites them directly demands a specific, documented response.
What to include in your appeal
Gather as many of these supporting documents as apply to your denial:
- –Explanation of Benefits (EOB)
- –Doctor's letter of medical necessity
- –Clinical notes and records from your provider
- –Prior authorization record (if applicable)
- –Summary of Benefits and Coverage (SBC)
See our submission guide for full instructions on each document and how to submit your appeal.
Related reading
Not legal or medical advice. Rebuttal is a document drafting tool, not a law firm. Review your letter before submitting and consult a licensed professional for legal questions specific to your plan.