GP, GO and GN: the Medicare therapy modifiers, and why a missing one costs you
Every outpatient therapy line on a Medicare claim says which kind of therapy it was. Leave that off and the line is denied, however good the care was.
One modifier on every therapy line
- GP: physical therapy
- GO: occupational therapy
- GN: speech-language pathology
Medicare wants one of these on every line delivered under a therapy plan of care, including the evaluation codes and the 97000-series treatment codes. A line without one is denied.
The modifier follows the plan of care
Use the modifier for the discipline whose plan of care the service is under, not the code's usual home. A therapeutic exercise code under an occupational therapy plan takes GO, even though physical therapists use the same code most of the time.
Assistants: CQ and CO
When a physical therapist assistant or occupational therapy assistant provides all or part of a service, Medicare wants CQ (physical therapist assistant) or CO (occupational therapy assistant) on that line as well. Medicare pays those lines at a reduced rate.
KX: past the yearly amount
Medicare sets a yearly amount for therapy. Above it, adding KX confirms that the therapy is still medically necessary and the notes support it. Physical therapy and speech-language pathology share one amount, and occupational therapy has its own.
Check before you send
Summit Practice Billing stops a Medicare therapy claim with a 97000-series line that has no GP, GO or GN before it goes out, so it's fixed once instead of appealed. Try your own codes in the free Claim Check.
Published October 29, 2026. Payer rules change, and Medicaid plans and insurers may differ from Medicare: check your payer's current policy before relying on any one rule here.
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