Comparison of three methods for the estimation of plasma antithrombin.

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Abstract
Plasma antithrombin levels were measured by clotting, immunological and amidolytic methods on 2 groups of subjects: 20 normal individuals and 9 patients studied serially post-operatively (hip replacement). The postoperative patients were observed for the emergence of deep-vein thrombosis using 125I-fibrinogen uptake measurements (FUT). The 3 methods gave similar ranges for the normal subjects, were reproducible (cv [coefficient of variability] < 5%), and detected early postoperative reduction of antithrombin levels. All 3 methods failed to show any significant differences in preoperative antithrombin levels between the positive and negative FUT groups. Correlation studies were performed on the pooled data from the normal and postoperative group (range 60-130% of normal; 100 samples). The best correlation (r [correlation coefficient] = 0.75; P < 0.01) was achieved with the chromogenic kit assay method vs the Mancini immunoassay technique. The thrombin agarose (total antithrombin) gel diffusion technique correlated less well with the chromogenic (r = 0.65; P < 0.01) and Mancini immunoassay (r = 0.45; P < 0.01) methods. The chromogenic kit method gives a rapid, reproducible and specific measurement of antithrombin III. The thrombin agarose diffusion method, though not specific for antithrombin III, is a cheap and simple method to perform. The potential of the 3 methods for detecting the prethrombotic stage and early thrombosis is discussed.