Accuracy of strain-gauge plethysmography as a diagnostic test in clinically suspected deep venous thrombosis.

Strain-gauge plethysmography (SGP) is currently employed in the diagnosis of deep venous thrombosis (DVT), but its accuracy has not been adequately tested. In this study we evaluated SGP against venography in 209 consecutive patients referred to us because of clinically suspected DVT of lower limbs. Venography was performed bilaterally if symptoms or signs suggesting DVT were present in both limbs. It was always performed after SGP and independently assessed. A total of 269 limbs could be evaluated with both SGP and venography, which disclosed DVT in 128 limbs of 110 patients. There were 109 proximal and 19 distal DVT. Out of the 128 limbs with DVT, SGP was positive in 114 (sensitivity = 89%) using Maximal Venous Outflow (MVO) as the diagnostic parameter, and positive in 116 (sensitivity = 91%) using an index obtained multiplying MVO for Venous Capacitance (VC). Out of the 141 venographically negative limbs, there were 6 false positive results using MVO and 9 using MVO X VC (specificity = 96% and 94% respectively). SGP sensitivity in acute proximal venous thrombosis was 97%, while it was about 60% in distal DVT. Most false positive results occurred in patients with edema of cardiac origin. SGP appears to be a useful diagnostic test in suspected DVT of lower limbs, particularly when both MVO and the index MVO X VC are used.