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Clotting inhibitors or anticoagulants; antithrombin III, activity

CPT4 code

Name of the Procedure:

Clotting Inhibitors or Anticoagulants; Antithrombin III, Activity Test


The Antithrombin III (AT III) activity test measures the activity level of antithrombin III, a protein that helps regulate blood clotting. This test is used to determine if a patient has a deficiency in antithrombin III, which can lead to abnormal clotting.


The antithrombin III activity test is used to identify if a patient has a deficiency in antithrombin III. The primary goal is to diagnose conditions that could lead to excessive blood clotting. This is essential for preventing complications like deep vein thrombosis (DVT) or pulmonary embolism (PE).


  • Unexplained blood clots
  • Family history of clotting disorders
  • Recurrent venous thromboembolism
  • Evaluation before starting long-term anticoagulant therapy
  • Screening for clotting disorders during pregnancy


  • No special preparation like fasting is typically necessary.
  • Patients may be advised to avoid certain medications such as heparin before the test.
  • A thorough medical history should be taken to identify any factors that could affect the test outcome.

Procedure Description

  1. Blood Draw: A sample of the patient's blood is taken, usually from a vein in the arm.
  2. Laboratory Analysis: The blood sample is sent to a lab where the activity level of antithrombin III is measured.
  3. Results Interpretation: The results are compared to normal ranges to determine if there is a deficiency.


The blood draw itself takes only a few minutes. Lab results may take a few days to be returned.


The procedure is performed in a hospital, outpatient clinic, or specialized diagnostic laboratory.


  • Phlebotomist or nurse for blood draw
  • Laboratory technicians to analyze the sample
  • Physicians (such as hematologists) to interpret results

Risks and Complications

  • Minor pain or bruising at the blood draw site
  • Rarely, infection or excessive bleeding
  • Misinterpretation if patient is on anticoagulant therapy at the time of testing


  • Accurate diagnosis of antithrombin III deficiency
  • Helps in tailoring appropriate anticoagulant therapy
  • Prevents severe complications like DVT or PE by enabling timely intervention


  • No specific recovery time is required post blood draw
  • Normal activities can be resumed immediately


  • Protein C and Protein S activity tests
  • Genetic testing for clotting disorders
  • Other coagulation tests (e.g., D-dimer test, Prothrombin time)

Patient Experience

  • Typically involves minor discomfort during blood draw
  • Minimal pain, akin to a standard blood test
  • Patients can expect little to no physical aftereffects from the procedure

Medical Policies and Guidelines for Clotting inhibitors or anticoagulants; antithrombin III, activity

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