Computerized strain-gauge plethysmography in the diagnosis of symptomatic and asymptomatic venous thrombosis

This study compares the results of a computerized strain-gauge plethysmograph with ascending lower limb venography in 94 patients with clinical deep venous thrombosis, and in 121 patients with asymptomatic legs being screened after total hip replacement. In the symptomatic patients, strain-gauge plethysmography had a sensitivity of 100%, an accuracy of 73%, a specificity of 64% and a negative predictive value of 100% for thrombosis above the popliteal confluence. In the screened patients, the figures were 38.1%, 55.4%, 60.0% and 81.1% respectively. Computerized strain-gauge plethysmography is a safe, non-invasive, reliable and portable method of excluding proximal thrombosis in a symptomatic patient. It avoids the need for urgent venography when anticoagulation therapy is reserved for those with proximal thrombosis. The device was not valuable as a screening tool after total hip replacement, since it had a low specificity and did not reliably detect the non-occlusive mural femoral thrombi which typically follow this procedure.