Overview
Modifier GP carries the CMS descriptor "services delivered under an outpatient physical therapy plan of care" and has been in the HCPCS file since January 1, 1999. It is one of three discipline modifiers: GO for occupational therapy and GN for speech-language pathology are the others. Chapter 5, section 20.1 of the Medicare Claims Processing Manual requires one of them on every line that reports a code from the applicable therapy code list, whether or not a financial limitation is in effect, and the Common Working File uses the modifier to count each beneficiary's therapy expenses toward the annual threshold. Physical therapy and speech-language pathology share one threshold and occupational therapy has its own, so the modifier decides which running total a service adds to.
The requirement is not limited to therapists. Physicians, nonphysician practitioners, therapists in private practice, rehabilitation agencies, comprehensive outpatient rehabilitation facilities, hospitals and skilled nursing facilities all report GP when they bill physical therapy under a plan of care. What the modifier cannot do is make a service therapy when it is not: the manual says the discipline modifiers never belong on codes outside the therapy list, so respiratory therapy or nutrition services are not reported with them, and a modifier does not let anyone furnish a service they are not qualified to furnish.
Institutional claims face extra edits. Lines with physical therapy revenue codes may carry only GP, only one discipline modifier is allowed per line, and evaluation and re-evaluation codes must carry the modifier of their own discipline. Contractors return institutional claims that break those rules. On professional claims, the most common errors are a missing modifier on a code that is always therapy and the wrong discipline modifier when a practice bills physical and occupational therapy on the same day.
GP also carries two companions. When a physical therapist assistant furnishes all or part of a service, CQ goes on the same line next to GP and Medicare pays that line at 85 percent. When a beneficiary's combined physical therapy and speech-language pathology expenses pass the year's threshold and the services remain medically necessary, KX is added to show the documentation supports continued therapy; above a higher amount, targeted medical review can apply. GP is the foundation for both, so a line missing it can distort the beneficiary's running totals as well as being returned. Because the modifier points to a plan of care, the services also have to fall under an established plan for that discipline that a physician or nonphysician practitioner has certified, as Medicare's outpatient therapy coverage rules require.
Worked example
A physical therapist in private practice evaluates a Medicare patient after knee replacement and starts a plan of care. The evaluation line and the therapeutic exercise lines on the claim each carry GP. Three weeks later a physical therapist assistant furnishes the exercise sessions under the same plan, so those lines carry GP and CQ. When the patient's combined PT and SLP expenses for the year pass the threshold and the therapist documents why therapy is still necessary, KX is added to the later lines as well.
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Frequently asked questions — Modifier GP (Physical Therapy Plan of Care)
Is GP required on every physical therapy claim line?
Yes, for Medicare. Chapter 5, section 20.1 of the Claims Processing Manual requires GP, GO or GN on every line that reports a code from the applicable therapy list, whoever bills it and whether or not the therapy threshold has been reached.
Can GP and GO be reported on the same line?
No. Each therapy line belongs to one plan of care, so it carries one discipline modifier. Contractors return institutional claims with more than one discipline modifier on a line or with a modifier that does not match the line's revenue code.
How does GP relate to the KX modifier?
GP tells Medicare that the service counts toward the combined physical therapy and speech-language pathology threshold. Once a beneficiary's expenses pass that amount, KX is added to show that continued therapy is medically necessary and documented.
Do physicians who bill therapy services need GP?
Yes. The modifier requirement applies to physicians and nonphysician practitioners billing physical therapy under a plan of care, as well as to therapists, agencies, hospitals and skilled nursing facilities.
Disclaimer
This glossary entry is operational reference for revenue-cycle and medical-billing professionals. It is not legal, clinical, or contractual advice. Industry benchmarks cite named public sources where available; always verify against the current guidance from the authority body before relying on a number in a contract, policy, or compliance filing.