Summary & Overview
CPT 85306: Free Protein S Level in Plasma
CPT code 85306 covers the laboratory measurement of free protein S in plasma, a specialized coagulation assay used to evaluate thrombotic risk and protein S deficiency. Nationally, this test is important for diagnosing inherited or acquired protein S deficiency, for workups of unexplained venous thromboembolism, and for guiding anticoagulation and hematology consults.
Key payers in the analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise explanation of the clinical purpose of the test, typical sites where it is performed, common modifiers associated with laboratory services, and notes on payer coverage patterns. The publication provides benchmark context for utilization and reimbursement where available and highlights policy or coding considerations that affect billing for specialized coagulation assays.
The content is intended for clinicians, laboratory managers, and revenue cycle professionals who need clear, nationally relevant information on how CPT code 85306 is used, what clinical situations prompt the test, and what operational points impact billing and claims processing.
Billing Code Overview
CPT code 85306 describes a laboratory test in which a lab analyst measures the free protein S level in a patient’s plasma. This assay evaluates the circulating free fraction of protein S, a vitamin K–dependent plasma protein that functions as a cofactor to activated protein C in regulating blood coagulation.
Service Type: Clinical laboratory testing
Typical Site of Service: Clinical laboratory or hospital laboratory
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Clinical & Coding Specifications
Clinical Context
A typical patient is a 32-year-old woman with a history of unprovoked deep vein thrombosis and a family history of thrombophilia who presents for a thrombosis workup. The clinician orders a free protein S antigen assay to evaluate for inherited or acquired protein S deficiency as a contributor to hypercoagulability. Blood is collected in a citrate tube and promptly delivered to the laboratory; centrifugation and plasma separation are performed, then the laboratory analyst runs the free protein S level assay (functional or antigen-based depending on lab platform). Results are reviewed by the ordering hematologist or coagulation specialist to correlate with concurrent anticoagulant use, acute phase reactions, pregnancy status, or liver disease. If abnormal, reflex testing such as total protein S, protein C, or genetic testing may be ordered and documented in the medical record. Typical site of service is an outpatient laboratory, hospital laboratory, or reference laboratory performing specialized coagulation testing.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when billing only the professional (interpretation) component of the test separate from the technical component. |
TC | Technical component |