Summary & Overview
CPT 85300: Antithrombin III Activity Assay
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.
Billing Code Overview
CPT code 85300 describes a laboratory procedure in which a lab analyst measures the activity of antithrombin III in a patient’s plasma. This test evaluates the functional level of antithrombin III, a key natural anticoagulant, and is used in clinical assessment of thrombotic risk and monitoring of coagulation disorders.
Service type: Laboratory diagnostic test (coagulation/hematology assay)
Typical site of service: Clinical laboratory or hospital laboratory
Data not available in the input.
Clinical & Coding Specifications
Clinical Context
A typical patient is an adult referred to the hospital laboratory for evaluation of a suspected thrombotic or bleeding disorder. A patient with a history of recurrent venous thromboembolism, unexplained thrombosis at a young age, or a new thrombotic event while on heparin therapy may undergo measurement of antithrombin III activity. The clinical workflow: a physician orders 85300 on the outpatient or inpatient laboratory requisition; a phlebotomist collects a citrate-anticoagulated plasma specimen; the specimen is transported to the clinical chemistry/hemostasis laboratory; a medical technologist or lab analyst performs a functional assay to determine antithrombin activity; results are reviewed by the laboratory director and reported to the ordering clinician, who integrates the result with clinical history, anticoagulant status (e.g., heparin, direct oral anticoagulants), and other coagulation studies (PT/INR, aPTT, D-dimer) to guide diagnosis and management.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
11 | Increased procedural service | When additional complexity or time was required by the lab beyond typical processing for 85300. |