What Is the FS Modifier and How Is It Used in Billing?

The FS modifier is a medical billing code applied to claims for specific healthcare services. Its primary purpose is to identify evaluation and management (E/M) visits that are “split or shared” between a physician and a non-physician practitioner (NPP) within the same group practice in a facility setting, such as a hospital. This modifier also indicates certain critical care services provided during the global period of an unrelated procedure.

Understanding the FS Modifier

A split or shared E/M visit occurs when both providers contribute to the same patient encounter on the same day. This allows for combined efforts to be billed appropriately, recognizing the involvement of multiple qualified healthcare professionals.

The modifier is also used for critical care E/M visits that occur during the global period of an operative procedure, provided the critical care is unrelated to the surgery. For instance, if a patient undergoes surgery and later requires critical care for a new, distinct medical issue, the critical care services can be reported with the FS modifier. This ensures that services distinct from the original procedure’s global package are appropriately identified and compensated. The Centers for Medicare & Medicaid Services (CMS) revised critical care billing rules effective January 1, 2023, allowing split or shared services and requiring the FS modifier.

Applying the FS Modifier

Applying the FS modifier correctly requires understanding what constitutes the “substantive portion” of a service. For split or shared E/M visits, the practitioner who provides the substantive portion of the visit bills the service. As of January 1, 2023, the substantive portion is primarily defined as more than half of the total time spent by both the physician and NPP on the E/M visit.

For critical care services, the practitioner who furnishes the substantive portion of the cumulative critical care time reports the service with the FS modifier. This means the practitioner who spent greater than 50% of the combined critical care time for CPT code 99291 or 99292 is the billing practitioner. If multiple practitioners report critical care time, the one with the most time reported for that patient on that day is the billing practitioner.

Comprehensive medical record documentation is necessary to support the use of the FS modifier. The documentation must clearly identify both providers involved and detail each provider’s contribution to the patient encounter. The billing provider must also sign and date the note, and the combined documentation of both the physician and NPP determines the billable level of service.

Compliance and Payer Policies

Medicare policies, established by the Centers for Medicare & Medicaid Services (CMS), largely dictate the application of this modifier. These policies are routinely updated, with significant revisions impacting split or shared services and critical care billing taking effect on January 1, 2023. The FS modifier helps Medicare identify how often services are split or shared and how frequently Medicare pays at the physician rate for services partially provided by NPPs.

While many private payers often align their policies with Medicare’s guidelines, it is not universally guaranteed. Other payers may have their own distinct policies or variations for using the FS modifier, or they may not recognize it at all. Providers should always consult individual payer policies to ensure proper billing and avoid claim denials.

Incorrect use of the FS modifier can lead to various consequences, including claim rejections and potential audits. Accurate and thorough documentation is important in supporting compliance. The medical record should clearly demonstrate that the services meet the specific criteria for using the FS modifier, detailing the contributions of each practitioner involved.