Summary & Overview
HCPCS C9091: Injection, sirolimus protein-bound particles, 1 mg
HCPCS Level II code C9091 denotes an injection of sirolimus protein-bound particles, 1 mg — an injectable formulation of sirolimus used in clinical settings requiring targeted immunosuppression or antiproliferative therapy. This code matters nationally as it standardizes billing for a specialized, unit-dosed biologic agent that may be used across oncology, transplant, and certain specialty care infusion settings. Accurate coding affects claims processing, coverage determinations, and provider reimbursement pathways for expensive injectable therapies.
Key payers addressed include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise overview of clinical context and the service setting, plus national benchmarking and policy-relevant considerations typically included in the full publication: utilization benchmarks, payer coverage patterns, coding and billing guidance, and any recent policy updates affecting reimbursement or prior authorization for injectable biologics. The summary highlights what providers and billing professionals need to know to code for the product accurately and to anticipate payer interactions. Where source data or payer-specific details are unavailable, the publication notes that information is not provided in the input.
Billing Code Overview
HCPCS Level II code C9091 describes an injection of sirolimus protein-bound particles, 1 mg. This service represents administration of a formulated sirolimus product delivered by injection.
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Service type: Injectable immunosuppressant therapy
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Typical site of service: Outpatient infusion clinic or hospital outpatient department
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Clinical & Coding Specifications
Clinical Context
A patient with recurrent or refractory cutaneous or systemic malignancy (for example, metastatic solid tumor or certain vascular tumors) is scheduled to receive an intravenous oncology formulation of sirolimus protein‑bound particles, billed as C9091 (injection, sirolimus protein‑bound particles, 1 mg). Typical patient is an adult oncology patient with central venous access (peripheral IV or port) receiving outpatient or inpatient infusion in an oncology infusion center, hospital outpatient department, or ambulatory surgical center. The clinical workflow includes: review of recent labs (CBC, CMP, renal and hepatic function), verification of indication and prescriber order, pharmacy reconstitution/dose calculation based on body surface area or mg dosing, sterile compounding under USP <797>/<800> as applicable, administration by an oncology‑trained RN with infusion monitoring, documentation of lot number and amount administered tied to C9091 units, and observation period for infusion‑related reactions. Typical sites of service are outpatient infusion center, hospital outpatient department, ambulatory surgical center, or inpatient acute care when clinically indicated. Patient scenarios may require modifier usage for services provided under unusual circumstances (for example, prolonged time, anesthesia involvement for procedural sedation, bilateral procedures if applicable to concurrent services) or payer‑specific reporting.
Coding Specifications
| Modifier | Description | When to Use |
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