Modifier 33 is a CPT^® modifier used to identify medical care whose primary purpose is delivery of an evidence based service, based on recommendations from the US Preventive Services Task Force.

Use when the USPSTF has given the service an A or B rating. These can be found here.

• When to use modifier 33
• Using modifier 33 indicates to the payer that the service is in accordance with the USPSTF recommendation
• The payer should process the claim without a patient due balance
• Be sure to use a screening diagnosis

From CPT^®:

Preventive Services: When the primary purpose of the service is the delivery of an evidence based service in accordance with a US Preventive Services Task Force A or B rating in effect and other preventive services identified in preventive services mandates (legislative or regulatory), the service may be identified by adding 33 to the procedure. For separately reported services specifically identified as preventive, the modifier should not be used.