Criteria in radioisotope detection of venous thrombosis.

Forty-one patients out of a larger series undergoing elective surgery were examined for the presence of venous thrombosis in the legs by means of the (125)I-fibrinogen technique. The radioisotope data were analysed by three different methods. The percentage uptake was calculated and, by the generally accepted difference of 15%, 22 patients had evidence of thrombosis. The statistical index, which takes account of the errors due to radioactivity counting inherent in the percentage uptake calculation, indicated thrombosis in 36 patients. The relative uptake index, which allows for the errors due to unequal distribution of radioactivity throughout the normal limb as well as the errors due to radioactivity counting, provided evidence of thrombosis in a total of 34 patients, compared with only 22 patients when assessed by the "15%" criterion.