Medicare Denied a Free Preventive Service

What This Means

Medicare covers many preventive services — like screenings, vaccines, and your annual wellness visit — at no cost to you, as long as you see a provider who accepts Medicare assignment. If you were denied coverage or charged money for a service you believe should have been free, something may have gone wrong with how it was billed.

This is one of the most likely types of denials to be resolved in your favor, because the issue is usually a billing or coding error — not a coverage decision. On your notice it often appears as CARC CO-96 (non-covered charges), even though the underlying service is a covered preventive benefit.

Why This Happens

• The service was coded as diagnostic instead of screening. This is the most common reason. If your provider used a diagnostic procedure code instead of the correct screening code, Medicare treats it as a regular service with cost-sharing rather than a free preventive service. For example, a screening colonoscopy should be billed with CPT code G0121 or G0105, but if the provider used code 45378 (diagnostic colonoscopy), you get charged. Similarly, a screening mammogram (code 77067) billed as a diagnostic mammogram (code 77066) triggers cost-sharing.
• The wrong modifier was used (or was missing). Medicare requires specific modifiers on preventive service claims. For example, screening colonoscopies require a PT or 33 modifier to indicate “preventive.” Without it, the claim may not be recognized as a screening. Ask your provider if the correct modifier was included.
• A screening converted to a therapeutic procedure. If a screening colonoscopy leads to a polyp removal, the coding gets more complex. Medicare is phasing out the coinsurance for this case: you pay a reduced 15% in 2023–2026 (instead of 20%), 10% in 2027–2029, and $0 starting in 2030. Billing errors — like charging the full 20% or omitting the PT modifier — are common here.
• You had the service more often than Medicare allows. Some preventive services are covered at specific intervals — for example, a screening mammogram once every 12 months, or a colonoscopy once every 10 years for average-risk patients. If you had the service sooner, Medicare may not cover it as a preventive benefit.
• The visit wasn’t coded as a wellness visit. Your annual wellness visit has its own billing codes. If the provider billed it as a standard office visit, you may be charged a copay.

Should You Appeal?

What To Do Next

1. Check whether the service is on Medicare’s covered preventive services list. Visit Medicare.gov’s preventive services page to confirm. If it’s on the list and you received it within the allowed time frame, you should not have been charged.
2. Call your provider’s billing office and ask them to check the coding. Specifically ask: “Was this billed with a screening code or a diagnostic code? Was the correct modifier (PT or 33) included?” In many cases, the billing office can correct the coding and resubmit the claim — no formal appeal needed.
3. Ask about the screening vs. diagnostic distinction. If you went in for a screening and it turned into a diagnostic or therapeutic procedure (like a polyp removal during a colonoscopy), make sure the PT modifier was applied so you get the reduced cost-sharing. For 2026 the correct patient share in that case is 15% coinsurance (phasing down to $0 by 2030) — not the full 20%, and not a denial.
4. If the provider won’t fix it, file an appeal. Write to the address on your denial notice, include a copy of the denial, and explain that the service is a Medicare-covered preventive benefit. Reference the specific service on Medicare’s covered list.
5. Contact 1-800-MEDICARE (1-800-633-4227) or your State Health Insurance Assistance Program (SHIP) if you need help. SHIP counselors can review your statement and help you determine if the billing was correct.

Sources

• Medicare.gov: Preventive and Screening Services — the covered list and $0 cost-sharing rules
• Medicare.gov: Colonoscopies (screening) — coverage intervals and the phased reduced coinsurance when a polyp is removed (15% in 2023–2026 → 0% in 2030)
• CMS: Preventive Services Coverage
• Medicare.gov: Your Guide to Medicare Preventive Services (PDF)
• CMS: Billing and Coding — Screening Colonoscopy Converted to Diagnostic/Therapeutic
• Medicare.gov: Your Medicare Rights & Appeals

Frequently Asked Questions