What are the types of antithrombin deficiency, and the clinical manifestations. What treatment options are available?
A normal AT range is assumed to be 80-120%. Individuals with low antithrombin levels have an increased thrombosis risk. The most common presentation of antithrombin deficiency is venous thrombosis of the lower limbs. A history of recurrent thrombosis occurs in about 60% of patients and is the clinical feature that usually prompts a search for AT deficiency.
AT deficiency is usually transmitted as an autosomal dominant trait in may in some countries affect up to 0.3% of the general population. In patients with a history of venous thrombosis presented before the age of 40-45, the incidence is estimated to be 3-5%. Levels of functionally active protein are usually around 40-70% of normal. There are two types of AT deficiency. Type I is the “classic” form of disorder and is characterized by a 50% reduction in both antigen and functional activity levels. Type II deficiency covers cases in which approximately half the plasma antithrombin is a variant protein with reduced activity. In other words, the antigen level is normal, but there is a mutation of the molecule that leads to decreased activity.
Acquired AT deficiency is also possible, and can be caused by such things as liver disease, DIC, and drugs. In some cases the risk of thrombosis is similar to that in hereditary AT deficiency. Acquired AT deficiency is usually accompanied by a decrease in other coagulation proteins, however, and is therefore difficult to determine an independent risk factor.
Management of AT deficiency includes the administration of heparin, warfarin, or antithrombin concentrates.