Antithrombin III (AT-III) Test

Norm of Antithrombin III (AT-III) Test

SI Units
Plasma 21–30 mg/dL 210–300 mg/L
85–115% of standard 0.85–1.15
>50% of control value
Serum 15–35% lower than plasma values
Immunologic 17–30 mg/dL
Functional 80–130%


Increased of Antithrombin III (AT-III) Test
Factor deficiency (V, VII), hemophilia (A, B), hepatitis (acute), inflammation, jaundice (obstructive), menstruation, nephrotic syndrome, renal transplantation, vitamin K deficiency. Drugs include anabolic steroids, androgens, bishydroxycoumarin, gemfibrozil, oral contraceptives (containing progesterone), progesterone, and warfarin sodium.
Decreased of Antithrombin III (AT-III) Test
Alcoholic liver disease, arteriosclerosis, burns, cardiovascular disease, cerebrovascular accident, carcinoma, cirrhosis, congenital antithrombin III deficiency, deep vein thrombosis, dengue shock syndrome, diabetes mellitus (type II), disseminated intravascular coagulation, hepatic disease (abscess, hepatitis), homocystinuria, hypercoagulation, liver failure (chronic), liver transplantation, malignancy (extensive), malnutrition, nephrotic syndrome, status post partial hepatectomy, postoperatively, postpartum, preeclampsia, pulmonary embolism, septicemia, thromboembolism, veno-occlusive disease (VOD). Drugs include estrogens, fibrinolytics, gestodene, heparin calcium, heparin sodium, L-asparaginase, methylprednisolone, and oral contraceptives (containing estrogen).


Description of Antithrombin III (AT-III) Test

A naturally occurring protein, IgG (immunoglobulin G), probably synthesized by the liver, that inhibits coagulation through inactivation of thrombin and other factors. The action of AT-III is catalyzed by heparin. Hereditary AT-III deficiency is an autosomal dominant disease that predisposes clients to venous thrombosis and heparin resistance.


Professional Considerations of Antithrombin III (AT-III) Test

Consent form NOT required.

  1. Tube: 2.7 or 4.5-mL blue topped.
  2. See Client and Family Teaching.



  1. Draw 2.4 mL of blood for a 2.7-mL tube or 4.0 mL of blood for a 4.5-mL tube.


Postprocedure Care

  1. Send the specimen to the laboratory for immediate spinning.


Client and Family Teaching

  1. Fast, except for water, for 10–12 hours before testing.


Factors That Affect Results

  1. Reject hemolyzed, lipemic, or contaminated specimens.
  2. Results are normally available within 3–5 days.


Other Data

  1. Levels of 50% to 75% indicate moderate risk for thrombosis, whereas levels under 50% indicate significant risk for thrombosis.
  2. A low level in clients taking warfarin indicates that the warfarin is not working effectively.
  3. AT-III is positively correlated to hematoma volume in hypertensive intracerebral hemorrhage (HICH).