 |
 |
Diagnosis
Making a Definitive Diagnosis of Hereditary AT Deficiency.
According to Dr. Moll and the National Alliance for Thrombosis and Thrombophilia, "A definitive diagnosis of hereditary ATIII deficiency (HD) is sometimes difficult to make because of ... interfering causes (that can temporarily depress circulating levels of antithrombin). Repeat testing ... to confirm low ATIII levels is always advisable to make a definitive diagnosis."
In the perfect case, a diagnosis of hereditary AT deficiency (the III in ATIII is no longer in common use) would be based on an established family history of venous thrombosis, decreased plasma AT levels taken at various time intervals, and the certain exclusion of acquired deficiency. However, such complete information is not always available.
When health professionals suspect hereditary AT deficiency they use tests or assays to measure AT levels. The normal range of AT in your blood reported by these tests can vary depending on the laboratory performing the test and the type of test performed. In general, an AT reading between 80-120% of normal is considered to be within normal limits.
Antithrombin is typically measured by two different methods: (a) the antithrombin antigen assay (a test that measures how much antithrombin is in your blood) and (b) the antithrombin activity assay, also called the functional antithrombin assay (that tests whether the antithrombin present in your blood actually works).
If an individual does not produce enough antithrombin, he/she has Type I HD, or quantitative deficiency. In this situation, both antithrombin test results are low. If an individual makes enough antithrombin, but the antithrombin does not work right, the person has Type II HD, or qualitative deficiency. This is caused by mutations that lead to the production of antithrombin molecules which are defective. In this case, antithrombin antigen levels are normal and activity levels are low.
Type II HD cannot be detected by an immunoassay. Therefore, both antigen and activity tests are necessary to differentiate Type I and Type II patients. This distinction is clinically important. Although Type II is more common than Type I, the risk of thrombosis is lower in most variants of Type II HD than in Type I patients.
Learn more about the AT gene and its mutations. 
References
Bauer, K. A. (1995)
Natural anticoagulants and the prethrombotic state In Blood: Principles and
Practice of Hematology, edited by R. I. Hardin, S. E. Lux, T. P. Stossel;
J. P. Lippincott Company, Phildadelphia.
Pp 1319-1339.
Conard, J., Horellou, M. H., van Dreden, P. Lecompte, T. Samama, M.
(1990) Thrombosis and pregnancy in congenital deficiencies in AT III, protein C or protein S:
study of 78 women. Thromb Haemost 63:319-320.
De Stefano, V., Leone, G., Mastrangelo, S., Tripod, A., Rodeghiero,F., Castaman, G., Barbui, T.,
Finazzi, G., Bizzi, B., Manucci, P. M.
(1994) Thrombosis during pregnancy and surgery in patients with congenital
deficiency of antithrombin III, protein C, protein S. Thromb Haemost 71:799-800.
Hellgren, M., Tengborn L., Abildgaard, U. (1982).
Pregnancy in women with congenital antithrombin III deficiency: experience of treatment with
heparin and antithrombin. Gynecol Obstect Invest. 14:127-141.
Pabinger, I., Schneider, B. (1996).
Thrombotic risk in hereditary antithrombin III, protein C, or protein S deficiency. A cooperative,
retrospective study. Gesellschaft fur Thrombose- und Hamostaseforschung (GTH) Study Group
on Natural Inhibitors. 16:742-748.
van Boven, H.H., and Lane, D. A.
(1997) Antithrombin and its inherited deficiency states. Seminars in Hematology 34:188-204.
|
|
