Antithrombin

Department of Haematology

Notes

• For Antithrombin testing as part of a full Thrombophilia screen, please see the Thrombophilia Screen test page.
• Test performed at GRH

Antithrombin (AT, formerly Antithrombin III) is a serine protease inhibitor. AT's main physiological action is against Thrombin, and it also acts against Factor Xa to a lesser degree. Antithrombin exerts a powerful and immediate inhibitory action on Thrombin when Heparin is present. AT deficiency can be congenital or acquired. Hereditary deficiency is associated with spontaneous thrombo-embolic disease, and is believed to account for 2-4% of cases of unexplained thrombosis in young adults. Acquired deficiencies may occur in liver disease, DIC, pregnancy, in prolonged Heparin therapy, Asparaginase therapy and in women taking Oestrogen-containing contraceptives. Oral anticoagulation may cause a rise in AT levels.

The AT molecule has two binding sites, one for Thrombin and one for Factor Xa. Deficiency can be as a result of a defect at one or both of these sites (qualitative, Type II deficiency) or as a result of reduced levels of otherwise normal AT (quantitative, Type I deficiency).

Sample Requirements

For Antithrombin analysis alone:

3ml or 3.5ml Trisodium Citrate sample

Sample Storage and Retention

• Pre analysis storage: do not store, send to laboratory within 2 hours.
• Sample retention by lab: Citrate samples are retained for a minimum of 24 hours at 15-30°C. If specialist coagulation tests are requested, one or more aliquots may be frozen until analysis (or up to two months) at between -15 and -40°C. After analysis, these samples will be retained for a further 24 hours at 15-30°C.

This test can be added on to a previous request as long as there is sufficient sample remaining and the sample is less than 4 hours old.

Turnaround Time

Antithrombin testing only: within 4 weeks

Reference Range