The Ratio of Functional: Immunologic Antithrombin III as an Index of Antithrombin Consumption

Abstract

In certain clinical conditions poor correlation between functional and immunologic antithrombin III (ATIII) may be an index of ATIII consumption. Plasma ATIII was measured in 50 controls and in 50 patients with acute pancreatitis (a) functionally using a chromogenic substrate assay and (b) immunologically using an immunodiffusion method. In the controls the functional ATIII range was 82-115% of the standard and the range of immunologic ATIII was 25-36 mg%. Functional and immunologic ATIII levels were significantly correlated in the controls and the range of the ratio of functional: immunologic ATIII was 3.08-3.66. 23 of the patients had a functional: immunologic ATIII ratio below 3.08 suggesting a relative loss of ATIII functional activity. In 7 of these 23 the functional ATIII level was reduced below the control range but in the other 16 functional ATIII was either high or within the control range and loss of functional activity was apparent only when functional and immunologic assays were compared. ATIII is an acute phase reactant. In certain clinical conditions (e.g. acute pancreatitis) consumption of ATIII may be overlooked if both functional and immunologic assays are not performed in parallel.