A type 1 antithrombin deficiency patient will present with which combination of antigen and activity?

A type 1 antithrombin deficiency patient will present with which combination of antigen and activity?

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

Answer: (C)

Antithrombin deficiency appears in two main forms: quantitative (less protein made) and qualitative (protein made but not working properly). In the quantitative form, there is less antithrombin protein in the blood, so the amount you measure as antigen is decreased and the functional activity is also decreased because there is simply less protein to perform its job of inhibiting thrombin and factor Xa. That means you see both reduced antigen and reduced activity. So the combination of decreased antigen and decreased activity corresponds to this quantitative type of deficiency. If the protein were present in normal amounts but not functioning, you’d have normal antigen with decreased activity, which is a qualitative defect. If both are normal, there’s no deficiency.

Antithrombin deficiency appears in two main forms: quantitative (less protein made) and qualitative (protein made but not working properly). In the quantitative form, there is less antithrombin protein in the blood, so the amount you measure as antigen is decreased and the functional activity is also decreased because there is simply less protein to perform its job of inhibiting thrombin and factor Xa. That means you see both reduced antigen and reduced activity.

So the combination of decreased antigen and decreased activity corresponds to this quantitative type of deficiency. If the protein were present in normal amounts but not functioning, you’d have normal antigen with decreased activity, which is a qualitative defect. If both are normal, there’s no deficiency.