In type 1 antithrombin deficiency, which combination of antigen and activity would you expect?

In type 1 antithrombin deficiency, which combination of antigen and activity would you expect?

• A. Normal antigen, normal activity
• B. Decreased antigen, decreased activity
• C. Decreased antigen, normal activity
• D. Normal antigen, decreased activity

Answer: (B)

In type 1 antithrombin deficiency you have a quantitative shortage of the AT protein. Because there is less antithrombin present, measurements of the protein level (antigen) are reduced, and the functional tests show reduced ability to inhibit thrombin and factor Xa as well. So the combination you’d expect is decreased antigen and decreased activity. By contrast, a qualitative defect (type II) would have normal antigen but reduced activity.

In type 1 antithrombin deficiency you have a quantitative shortage of the AT protein. Because there is less antithrombin present, measurements of the protein level (antigen) are reduced, and the functional tests show reduced ability to inhibit thrombin and factor Xa as well. So the combination you’d expect is decreased antigen and decreased activity. By contrast, a qualitative defect (type II) would have normal antigen but reduced activity.