Diagnostic leg scanning for deep venous thrombosis in the recently heparinized patient

Leg scanning with fibrinogen I 125, either alone on in combination with other procedures, has been proposed as an alternative to venography for diagnosis of deep venous thrombi. Clinical circumstances may necessitate anticoagulation before scanning can be performed, which could alter its reliability. We have compared the results of scanning with venographic findings in heparinized patients with venous thromboembolism. Different criteria for an abnormal leg scan gave different sensitivities and specificities. During the first four days of scanning with a requirement for a persistently abnormal result, five of eight criteria had high specificity (greater than 92%). However, sensitivities did not exceed 55%. With the use of transiently abnormal results and six days of scanning, higher sensitivities were obtained but specificities were reduced. No criterion gave results considered acceptable for a diagnostic test for deep venous thrombosis. Leg scanning should therefore not be used for this purpose in patients who have received anticoagulants. Our results also suggest that duration of symptoms has little effect on the sensitivity of leg scanning and that the test is more reliable for establishing the presence of thrombus than at defining its location.