CO-55: Procedure/Treatment Deemed Experimental/Investigational

What Does CO-55 Mean?

With CO (Contractual Obligation), the CARC 55 denial for procedure/treatment deemed experimental/investigational is the provider's contractual responsibility. The patient is not liable for this amount. However, the provider may appeal with supporting clinical or administrative documentation if the denial is believed to be in error.

CARC 55 indicates procedure/treatment deemed experimental/investigational. The payer determined that the service or a portion of it does not meet coverage criteria under the patient's current plan benefits or the applicable coverage rules.

Common scenarios that trigger this adjustment include: the payer's medical policy classifies the procedure, treatment, or drug as experimental or investigational; The payer determined there is insufficient clinical evidence that the treatment is effective for the patient's condition; Drug or device is used off-label for an indication not approved by the FDA. The group code paired with CARC 55 determines who bears the financial responsibility — CO places it on the provider as a contractual obligation, PR shifts it to the patient, OA indicates a coordination of benefits or other payer adjustment.

Common Causes

How to Resolve

1. Review the denial Examine the CO-55 denial and any RARC codes to understand the specific basis for the coverage determination.
2. Gather supporting documentation Collect medical records, clinical notes, authorization documents, or other evidence that supports the medical necessity or coverage of the denied service.
3. File the appeal Appeal with peer-reviewed clinical studies, FDA approvals, professional society guidelines, and clinical trial results supporting the treatment. Include a letter from the treating physician explaining the medical necessity and why this treatment is the most appropriate option. Request a peer-to-peer review for complex cases.
4. Track the appeal outcome Monitor the appeal status and follow up as needed. If denied again, consider further levels of appeal if available.

Common RARC Pairings

The RARC code tells you exactly what triggered the CO-55:

How to Prevent CO-55

• Check payer medical policies before performing new or novel treatments
• Obtain prior authorization for treatments that may be classified as experimental
• Stay current on payer coverage updates for evolving treatments
• Communicate with payers about coverage criteria before treatment

Also Filed As

The same CARC 55 may appear with different Group Codes:

Related Denial Codes