Standardisation of a simple method for the determination of antithrombin activity

SUMMARY A procedure is described for performing a functional assay of serum antithrombin activity. The method consists of adding serum to a thrombin solution and measuring, after a fixed incubation time, the residual thrombin activity on a substrate plasma. The mean serum anti-thrombin activity found in 96 healthy blood donors using this procedure was 109-5 % (range 82 %-160 %). The method was linear over an activity range between 30-5 % and 176%, was significantly correlated with antithrombin-III protein concentration determined by radial immunodiffusion (r = 0.86, P <00 1), and showed good reproducibility (coefficient of variation 2-7 %). On account of its simplicity and precision this functional assay should be of considerable use in evaluating hypercoagulability. Over the years the attention of pathologists has been directed almost exclusively to the bleeding disorders of blood coagulation, and every effort has been made to develop laboratory tests designed for the diagnosis of clotting factor deficiencies. Recently, however, it has become evident that the concentra