Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (727 page)

   Limitations

   Minimum specimen volume for microscopic analysis is 0.1 mL.

Suggested Reading

Bohring C, Krause W. Immune infertility: towards a better understanding of sperm (auto)-immunity. The value of proteomic analysis.
Hum Reprod.
2003;18:915–924.

ANTITHROMBIN (AT)
*

   Definition

   AT, also known as antithrombin III, is a natural inhibitor of thrombin and of other clotting factors essential in the coagulation cascade. It is synthesized in the liver. In the presence of heparin, the activity of AT is enhanced approximately 1,000 times.

   
Normal range (for functional activity):
75–125%. The functional assay can be performed in a clot detection system or in a chromogenic one. The antigen normal range is the same as for the functional assay, but the assay is rarely necessary in clinical practice.

   Use

   Because deficiency of AT may result in a thrombophilic syndrome, determination of AT is indicated in cases suspected of congenital thrombophilia. It is also of help in determining the prognosis in disseminated intravascular coagulation (DIC) because levels become markedly decreased in severe cases.

   Interpretation

   Acquired deficiencies have been reported in severe liver disease, some malignancies, use of oral contraceptives, nephrotic syndrome, and severe infections, especially if associated with DIC (the assay is useful in determining the severity of DIC: it decreases in parallel with increasing severity of the syndrome).

   AT is not affected by deficiency in vitamin K or by vitamin K antagonists.

   It decreases during heparin therapy.

   Severe deficiency may result in diminished anticoagulant effect of heparin.

   Limitations