Imperial Collage Healthcare

Antithrombin level

Lab Code : ATACT- usually ordered as part of a thrombophilia screen

Test Background
Antithrombin has a powerful anticoagulant action in the presence of heparin, working by neutralising serine proteases, particularly thrombin and Xa. It acts more strongly against thrombin in the presence of higher molecular weight heparins, and against Xa with lower molecular weight heparins. A hereditary deficiency of antithrombin is accompanied by a high frequency of spontaneous thrombotic disorders. Hereditary antithrombin deficiencies are quantitative (type I) or qualitative (type II). The incidence of inherited deficiency has been estimated at between 1:2,000 and 1:5,000 in the normal population. In addition, a number of acquired deficiencies have also been described. An antithrombin antigen ELISA is available to distinguish between type I or type II where the antithrombin activity is abnormally low.

Clinical Indications
Venous thromboembolism at a young age (including childhood) Recurrent venous thromboembolism Unusual site of thrombosis (eg. mesenteric, renal, portal veins, cerebral venous sinuses) Thrombosis during pregnancy or puerperium Recurrent superficial thrombophlebitis Arterial thrombosis at a young age (abruptio placentae, pre-term delivery) Neonatal purpura fulminans or massive thrombosis in newborn Perthe's disease of the lip Warfarin-induced skin necrosis.

Reference Range

                                         Antithrombin Activity           
Adult > 16 years                    0.66 - 1.24 IU/mL            
Paediatric (11-16 years)         0.96-1.26 IU/mL 
Paediatric (6-10 years)          0.95-1.34 IU/mL 
Paediatric (1-5 years)            1.01-1.31 IU/mL 
Paediatric (Day 4 - 1year)      0.72-1.34 IU/mL 
Paediatric (Day 2 - Day 3)      0.60-0.89 IU/mL 
Paediatric (Day 0 - Day1)       0.58 - 0.90 IU/mL                  

Antithrombin Antigen 0.79 - 1.11 IU/mL

Sample Required
2.7 mL sodium citrate (pale blue top) adults 1.8 mL sodium citrate (pale blue top) paediatrics

Turnaround Time
14 days

Special handling: avoid prolonged stasis during venepuncture. Sample must be received by lab within 2 hours of collection. Samples will be rejected if under/over-filled, clotted or haemolysed or if patients are receiving anticoagulant therapy. Similarly, sampling is inappropriate within 4 weeks post-childbirth or during an acute phase inflammatory response. A discussion with a haematologist is advisable prior to requesting this and other thrombophilia tests. Requests may be subject to approval by haematology prior to testing.

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