Combined use of strain-gauge plethysmography and latex D-dimer test in clinically suspected deep venous thrombosis

Abstract

The diagnostic value of a latex D-dimer test combined with strain-gauge plethysmography (SGP) was assessed in 425 patients referred to our vascular laboratory because of clinically suspected deep-vein thrombosis (DVT) of lower limbs, using venography as the reference standard. The inpatient/outpatient ratio was 236 189 . Adequate venograms were obtained in 401 patients and a DVT was diagnosed in 195 (49%). SGP results were borderline in 38 patients. In the 363 unequivocal cases, sensitivity of SGP was 88% and specificity 90%. The sensitivity of D-dimer latex test was 78% and the specificity 88%. Out of the 363 unequivocal cases, D-dimer test results were discordant with SGP in 88 cases, of whom 60% had DVT and 40% had not, and concordant in 275. The sensitivity of concordant results was 98% ( 124 127 ) and specificity 97% ( 143 148 ). Compared with strain-gauge plethysmography (plus venography in case of borderline results), the combined approach reduced the diagnostic errors (false positive plus false negative results) from 10% ( 40 401 ; 95% confidence interval, 7–13%) to 2% ( 8 401 ; 95% CI, 0.6–3.4%) albeit requiring a greater number of venographies, from 9% ( 38 401 ; 95% CI, 7–12%) to 31% ( 126 401 ; 95% CI, 27–36%). Most calf DVT (94%) were identified. We conclude that this test combination is valuable in the diagnosis of DVT in symptomatic patients, because of the high accuracy of concordant test results. Venography is required in case of borderline or discordant results.