CPT code 85300 represents a laboratory assay that measures antithrombin III activity in a patient’s plasma, a clinically important test for evaluating anticoagulant function and thrombotic risk. Nationally, this assay supports diagnosis and management of coagulation disorders, perioperative assessment, and monitoring of patients on anticoagulant therapy. The code is used by hospital and clinical laboratories and is relevant to clinicians in hematology, surgery, and internal medicine.

Key payers discussed include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find an overview of clinical context for ordering the test, typical sites of service, and the payer landscape that affects coverage and billing practices. The publication summarizes benchmarks where available, notes common billing modifiers and coding considerations, and highlights policy and reimbursement updates that influence laboratory billing for coagulation testing.

The article provides practical clarity about when CPT code 85300 applies, which clinical scenarios commonly prompt the test, and how payers typically approach coverage. Data not available in the input is noted explicitly in relevant sections.