Billing Code Overview

HCPCS Level II code S9131 represents physical therapy provided in the home on a per diem basis. This code describes a miscellaneous, non-facility service line for skilled physical therapy delivered in a home setting where billing is reported as a daily (per diem) charge. The service type is Physical Therapy (HCPCS Level II miscellaneous service). If additional billing details or service-line metadata are required, Data not available in the input.

Clinical Context

A typical patient is an older adult receiving skilled services at home for mobility and functional limitations following an acute exacerbation of chronic low back pain with associated knee pain and generalized weakness. The home health agency schedules a per diem physical therapy visit billed with HCPCS Level II code S9131 for direct treatment in the home setting. The clinical workflow includes an initial home evaluation by a physical therapist or rehabilitation practitioner to establish a plan of care, implementation of therapeutic exercises, neuromuscular reeducation, and functional task training during the per diem visit, documentation of daily progress and safety assessment, and coordination with the referring physician for updates to the plan of care and any changes in frequency or discipline.

Coding Specifications

• Modifiers listed:

• GN: Services delivered under an outpatient speech-language pathology plan of care — used when the billed per diem home-based service is provided under a speech-language pathology plan of care.

• GO: Services delivered under an outpatient occupational therapy plan of care — used when the billed per diem home-based service is provided under an occupational therapy plan of care.

• Provider taxonomies and specialties:

• Notes:

• Use the modifier that corresponds to the discipline and plan of care under which the per diem service is delivered. No additional modifiers are provided in the input.

Related Diagnoses

• M54.5 — Low back pain

  Low back pain is a common primary complaint driving home-based physical therapy per diem services for pain management, mobility training, and functional improvement.

• M25.561 — Pain in right knee

  Right knee pain can limit ambulation and transfers, prompting therapeutic interventions and functional training delivered during a home per diem visit billed with S9131.

• M62.81 — Muscle weakness (generalized)

  Generalized muscle weakness contributes to reduced functional endurance and safety risks; it is a frequent indication for skilled physical therapy delivered in the home under a per diem model.

• R26.2 — Difficulty in walking, not elsewhere classified

  Difficulty walking is a direct functional problem addressed by gait training, balance activities, and therapeutic exercises provided during per diem home therapy.

• G81.90 — Hemiplegia, unspecified affecting unspecified side

  Hemiplegia indicates significant unilateral weakness and functional impairment; home-based per diem physical therapy often focuses on mobility, transfers, and compensatory strategies for these patients.

Related Codes

• Relationship to HCPCS Level II code S9131:

• 97110: Provides targeted strengthening and range-of-motion interventions that may be delivered during a per diem home therapy visit billed with S9131.

• 97112: Describes neuromuscular reeducation interventions that can be part of the skilled therapeutic content provided during the per diem S9131 visit.

• 97530: Represents task-oriented therapeutic activities that commonly occur during a home per diem session and may be billed in conjunction with or documented as part of services captured by S9131 depending on payer guidance.

• 97750: Functional performance testing that may be performed during or adjacent to a per diem home therapy episode and documented to support the need for continued skilled therapy.

• Common pairings/alternatives: 97110, 97112, and 97530 are commonly used together to describe the skilled components provided during a home therapy day billed under S9131. 97750 is commonly used as an assessment adjunct to document functional status changes.

National mean rates for HCPCS Level II code S9131 show BUCA (average commercial) with a higher mean ($84.10) compared with Medicare (reported as $0.00 in the input). Cigna Health posts the highest commercial mean among listed payers at $97.87, while Aetna and Blue Cross Blue Shield sit near the mid-70s.

Dispersion (P75 minus P25) varies notably across payers. Blue Cross Blue Shield and UnitedHealthcare display the widest spread (74 and 122 percentage points respectively when comparing the 75th and 25th percentiles), indicating substantial variability. Cigna Health and Aetna are the tightest, with effectively no spread for Cigna (0 points) and a 0.33-point spread for Aetna. The table and chart below present the full breakdown.