CPT Modifier 33

What modifier 33 means

Modifier 33 identifies that the primary purpose of the service was the delivery of an evidence-based preventive service — one rated A or B by the U.S. Preventive Services Task Force (USPSTF) or otherwise mandated under the Affordable Care Act. Appending it tells a non-grandfathered commercial plan to waive patient cost-sharing (deductible, copay, coinsurance). It also preserves preventive cost-sharing protection when a screening service becomes diagnostic or therapeutic during the same encounter.

When to use it

Append to a preventive service (e.g., a screening colonoscopy) on a commercial/ACA plan, or when a screening procedure converts to therapeutic in the same session (such as a polyp removed during a screening colonoscopy) and you want the patient's preventive cost-sharing waiver to carry over.

Documentation checklist

The record should support every item below before you append modifier 33.

• Order or note establishing the service was performed with screening (preventive) intent
• The USPSTF A/B recommendation or ACIP/ACA basis supporting the preventive designation
• If screening converted to therapeutic, the finding and procedure that triggered the conversion
• Patient eligibility for the preventive benefit (age/risk per the recommendation)

Do NOT use modifier 33 when

• The service is not a USPSTF A/B (or ACA-mandated) preventive service
• The encounter was diagnostic from the outset (the patient was symptomatic)
• Billing Medicare for a screening colonoscopy that becomes diagnostic — Medicare instructs modifier PT, not 33

Common denial reasons

• Applied to a service not on the USPSTF A/B / ACA preventive list
• Plan is grandfathered or self-funded and not subject to the ACA preventive mandate
• Cost-sharing still applied because the diagnosis coded the visit as diagnostic, not screening

How to appeal a modifier 33 denial

Cite the ACA preventive-services mandate and the specific USPSTF A/B rating (or ACIP recommendation) for the service, and attach the order showing screening intent. For a screen-turned-therapeutic colonoscopy, include the pathology/operative note demonstrating the encounter began as a screening so the cost-sharing waiver is preserved.

Payer notes

Modifier 33 applies to non-grandfathered commercial plans under the ACA. Traditional Medicare does not use 33 for a screening colonoscopy that turns diagnostic — it uses modifier PT for that scenario. Always confirm whether the specific plan is ACA-subject.

Related & commonly confused modifiers

Where modifier 33 is used

• Preventive medicine E/M (99381–99397)
• Screening colonoscopy (G0121, 45378–45385)
• Immunization administration (90471–90472)