These services are not covered under the patient benefit plan (Updated for 2026)

Common Causes for CO-166

Denials with code CO-166 typically happen for the following specific reasons:

• Billing for services classified as cosmetic, experimental, or investigational under the payer's medical policy guidelines.
• Performing routine or preventive services that exceed the specific frequency limits or age restrictions defined by the patient's insurance plan.
• Failing to verify plan-specific exclusions during the pre-registration and insurance eligibility verification process.
• Rendering specialized care (such as acupuncture, genetic testing, or weight loss programs) that is completely excluded from the employer-sponsored benefit package.

How to Prevent CO-166 Denials

To avoid receiving this denial in the future, implement these specific checks:

• Conduct comprehensive real-time eligibility (RTE) verification prior to the patient encounter to check for plan-specific exclusions and limitations.
• Secure a signed Advance Beneficiary Notice (ABN) for Medicare patients, or a commercial non-covered service waiver, to establish patient financial responsibility before rendering non-covered services.
• Implement automated billing system edits that flag historically non-covered CPT/HCPCS codes based on the patient's specific payer plan ID.
• Provide financial counseling to patients prior to scheduling elective or non-covered procedures, ensuring they understand their out-of-pocket liabilities.

Appeal Letter Template for CO-166

If you believe this claim was denied incorrectly, you can use the following template to submit an appeal.

[Your Practice Header]
[Date]

[Payer Name]
[Appeals Department Address]

RE: Appeal for Claim [Claim Number]
Patient: [Patient Name]
ID: [Patient ID]
Date of Service: [Date]
Denial Code: CO-166 - These services are not covered under the patient benefit plan

Dear Appeals Department,

I am writing to appeal the denial of the above-referenced claim, which was denied with code CO-166: "These services are not covered under the patient benefit plan".

We are appealing the denial of claim number [Claim Number] for CPT/HCPCS code [CPT Code] under denial code CO-166. While we acknowledge the payer's standard policy exclusions, the clinical documentation enclosed demonstrates that this service was not elective, cosmetic, or experimental, but rather a medically necessary intervention required to treat the patient's severe [insert diagnosis/condition]. According to AMA CPT guidelines and established clinical standards, this service constitutes the primary standard of care for this diagnosis and should be evaluated under individual medical necessity provisions rather than a generic benefit exclusion. We respectfully request a clinical peer review of the attached medical records and objective diagnostic findings, and ask that this denial be overturned and approved for reimbursement.

Attached please find:
1. A copy of the original claim.
2. The relevant medical records supporting the service.
3. [Any other supporting documents].

We respectfully request that you reprocess this claim for payment.

Sincerely,

[Your Name]
[Title]
[Practice Name]