AIR PLETHYSMOGRAPHY IN THE DETECTION OF SUSPECTED ACUTE DEEP-VEIN THROMBOSIS

Aim: To test the value of outflow fraction using air plethysmography ( APG) in the detection of suspected acute deep vein thrombosis (DVT) ex tending proximal to the calf. Design: Prospective study in patients an d normal volunteers. Setting: Academic Surgical Unit and Vascular Unit , St Mary's Hospital Medical School, London, UK. Material and methods: We prospectively examined 152 lower extremities of 150 patients with clinical suspicion of DVT. Patients were examined by APG (outflow frac tion) and either ascending venography or colour flow duplex imaging (C FDI) as gold standards to establish the diagnosis. The reproducibility of outflow fraction was tested in two normal volunteers and was shown to have coefficients of variation of 6.1% and 8.2%, respectively. Res ults: On venography or CFDI, DVT was detected in 96 limbs. Proximal DV T was seen in 74; it was confined to the calf in 22. APG was 95% sensi tive, 95% specific and 95% accurate in detecting proximal DVT whereas it was 45% sensitive, 95% specific and 81% accurate for calf DVT. Conc lusions: Using air plethysmography, the outflow fraction is a highly r eproducible and accurate measurement in detecting DVT proximal to the calf. The high positive predictive value means that if the test is pos itive, treatment can start immediately; if it is negative, duplex scan ning is necessary to exclude proximal partially occluded thrombi or ca lf DVT.