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.