Activity and Concentration of Antithrombin III in Plasma and Serum

The concentration and activity of antithrombin III contained in plasma and serum of a single individual were compared with each other. The concentration of antithrombin III was determined by means of the rockett technique according to Laurell, antithrombin activity was measured by thrombin neutralization, residual thrombin activity was quantified using the chromogenic substrate Chromozym TH. The patients’ plasmas examined could be divided into different groups according to their antithrombin III specific activity. Most of the samples contained about 34 U/mg, the specific activities of two other groups were about 20 u/mg and 15 U/mg respectively. Only 3 samples contained more than 45 U/mg. In plasma samples with low specific antithrombin III activity the simultaneous occurrence of free antithrombin and an antithrombin-thrombin complex formed in vivo has been demonstrated by means of the two-dimensional Immunoelectrophoresis with heparin added to the agarose-gel medium. (Sas et al., 1975). The antithrombin-thrombin complex could be separated from free antithrombin by adsorption to a heparin-agarose column and fractionated elution, using the different heparin affinity of complex-bound and free antithrombin.