The thrombin-inactivating α₂-globulin, antithrombin III (At-III), was measured in plasma and urine with a chromogenic tripeptide substrate, using a centrifugal analyzer. Plasma At-III was subnormal in liver disease. In acute myocardial infarction a mean At-III of approximately 120% of normal was found. At-III in persons who developed deep-vein thrombosis decreased significantly (p < 0.05) between the day of admission and the 3rd day after admission to hospital. Urine from normals did not contain detectable At-III. With increasing urinary albumin increasing concentration of At-III was found.

SummaryAntithrombin III (At-III) was measured at the time of admission and two days later in 131 patients laid up in a coronary care unit. The patients were examined for deep-vein thrombosis (DVT) clinically and by means of 125I-fibrinogen scanning. 19 patients developed DVT. In 11 subjects with and 25 without DVT At-III decreased more than 10%. And in 7 with and 17 without DVT At-III decreased more than 15%. One person with DVT had subnormal At-III. By using decrease of At-III or subnormal initial At-III to predict DVT the following predictive value (PV) were found. Decrease ≤ 10%, PV pos.= 0.32 and PV neg. = 0.93. Decrease ≤ 15%, PV pos. = 0.32 and PV neg. = 0.90. The positive predictive values obtained were too low to let decreasing At-III give occasion for prophylactic anticoagulant treatment.

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