The short answer
Medicare Part B applies a payment reduction to certain outpatient physical therapy services furnished in whole or in part by a physical therapist assistant. CMS uses the CQ modifier to identify applicable PTA-furnished services. For claims subject to the policy, payment is 85% of the otherwise applicable amount.
The reduction is not triggered simply because a PTA participated in a visit. CMS’s de minimis policy considers the portion of a service independently furnished by the assistant. The modifier and payment treatment depend on the service, the minutes furnished independently, and whether the therapist’s own work meets the applicable timed-service threshold without counting the assistant’s minutes.
What a billing team should check
Before submitting an affected claim, confirm the date of service, discipline, plan of care, service line, minutes attributable to the PTA, and the documentation supporting the work performed. Check whether the CQ modifier applies to that service line and whether the corresponding therapy modifier is present. Use current CMS instructions and examples; do not apply the rule based on a general note that a PTA was involved.
For timed services, CMS examples explain how the de minimis policy interacts with the midpoint rule. The therapist’s minutes may independently meet the billing threshold even when the PTA also contributed. If they do not, the CQ modifier may apply under the policy. Each service line needs to be evaluated using the applicable CMS rules and documentation.
Keep the scope narrow
This is a Medicare outpatient PT payment overview, not a complete guide to supervision, documentation, state practice acts, commercial payer policies, or every therapy setting. Occupational therapy has a parallel CO modifier for OTA-furnished services; this article focuses on PTAs. Commercial plans may use different rules. Confirm the applicable policy for the payer, setting, and date of service.
How Brace Health fits
Brace Health’s billers help practices investigate claim details and payer responses. The practice and treating professionals remain responsible for accurate clinical documentation and code selection. A billing team should surface a possible modifier or payment issue for review, not infer clinical facts or change a supported claim without the appropriate confirmation.