Healthcare providers use Current Procedural Terminology (CPT) modifiers on billing claims to provide specific information about a service or procedure, ensuring accurate reimbursement from payers like Medicare. These two-character codes are attached to CPT or Healthcare Common Procedure Coding System (HCPCS) codes to signify that the service performed was altered by specific circumstances. Modifier GO is a specific identifier used in therapy services billing, signaling to the payer that the reported services fall under an occupational therapy plan of care.
Defining Modifier GO and Its Purpose
Modifier GO is officially defined by the Centers for Medicare & Medicaid Services (CMS) as “Services delivered under an outpatient occupational therapy plan of care.” This modifier is a component of Medicare Part B billing for rehabilitation services. Its primary function is to distinguish occupational therapy services from those provided by other disciplines, such as physical therapy or speech-language pathology.
The use of GO ensures that the claims processing system accurately categorizes the service, matching it to the correct payment rules and documentation requirements. It must be present on a claim line for all covered occupational therapy procedures, regardless of whether a therapist or an assistant performed the service. The presence of GO signals that the service is delivered by an Occupational Therapist (OT) or under the supervision of one.
Applicability: Which Therapy Services Use GO?
Modifier GO is exclusively applicable to services provided under an Occupational Therapy plan of care. This includes all timed and untimed CPT/HCPCS codes used to bill for therapeutic procedures, evaluations, and modalities. It applies across various outpatient settings where Medicare Part B covers therapy, such as hospital outpatient departments, skilled nursing facilities, comprehensive outpatient rehabilitation facilities (CORFs), and private practice offices.
When a Certified Occupational Therapy Assistant (COTA) provides the care, the GO modifier must be submitted alongside the specific assistant modifier, CO, on the same service line. This pairing signals to Medicare that the services were furnished, in whole or in part, by the assistant. The GO modifier serves as the discipline-specific anchor for all occupational therapy services.
The Financial Impact of Using Modifier GO
The financial consequence of services identified under a GO plan of care arises when the assistant modifier, CO, is also applied. This mandatory payment differential was established by Section 53107 of the Bipartisan Budget Act of 2018 (BBA) and took effect on January 1, 2022. This legislation requires a payment reduction for outpatient therapy services provided by a therapy assistant.
The rule mandates that services furnished in whole or in part by a COTA are reimbursed at 85% of the rate paid for the same services when furnished by the occupational therapist. The reduction is triggered when the COTA provides more than 10% of the total time for a service unit, often referenced as the de minimis standard or the 8-minute rule for timed codes. If an occupational therapy service meets this threshold, the claim must include both the GO and CO modifiers to reflect the lower payment rate.
For example, if a provider bills for one 15-minute unit of therapeutic activity, and a COTA provides at least eight minutes of that service, the GO and CO modifiers must be paired. This signals to the Medicare system that the payment for that specific unit must be reduced by 15%. This policy aligns the reimbursement for therapy assistants with the model used for other non-physician practitioners, such as physician assistants.
When the occupational therapist provides the service entirely, or the COTA’s involvement falls below the de minimis threshold, only the GO modifier is used, and the provider receives the full 100% payment rate. The GO modifier establishes the context for whether the CO modifier and the associated 15% payment reduction are necessary. This distinction aims to achieve budget savings within the Medicare system by differentiating between services provided by the therapist versus the assistant.
Documentation and Auditing Requirements
The requirement for the GO and CO modifiers places an administrative burden on therapy providers to ensure compliance and avoid payment penalties. Providers must maintain detailed patient records that clearly document which personnel, the OT or the COTA, performed each specific service. This notation must include the exact time spent by each provider on all timed CPT codes.
Auditors rely on this documentation to verify that the CO modifier was applied correctly whenever the COTA’s time exceeded the de minimis threshold. Insufficient or contradictory documentation can lead to claims being denied or recouped during an audit. The accurate pairing of GO with CO, based on precise time-tracking, is the primary mechanism for demonstrating adherence to the mandatory 85% payment differential rule.