By Brandon Seigel, Chief Problem Solver · September 2, 2026 · 7 min read
Discipline modifiers: GP, GO, GN
Medicare requires a modifier that tells the payer which plan of care the service falls under:
- GP — physical therapy
- GO — occupational therapy
- GN — speech-language pathology
NCCI edits: 59 and the X modifiers
Some code pairs can't normally be billed together — 97140 with 97530 is a well-known example. When the services were truly separate and distinct, modifier 59 or a more specific X modifier (XE, XS, XP, XU) tells the payer why. Using them without support is a top audit target.
KX: above the therapy threshold
KX confirms medical necessity for Medicare care above the annual therapy threshold.
CQ and CO: assistants
When a PTA (CQ) or COTA (CO) furnishes a service in whole or in more than 10% of its minutes, Medicare requires the modifier and pays that service at 85% of the fee schedule. Accurate de minimis tracking protects both compliance and revenue.
Quick answers
What does the GP modifier mean?
GP indicates the service was delivered under a physical therapy plan of care. GO is used for occupational therapy and GN for speech-language pathology.
When is the CQ modifier required?
When a physical therapist assistant furnishes a service in whole or for more than 10% of the service's minutes, for Medicare patients.
Sources and further reading
See exactly what's included in our medical billing services for therapy practices, how our percentage-of-collections pricing works, or browse common questions from practice owners.
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