COMBINED USE OF STRAIN-GAUGE PLETHYSMOGRAPHY AND LATEX D-DIMER TEST IN CLINICALLY SUSPECTED DEEP VENOUS THROMBOSIS

The diagnostic value of a latex D-dimer test combined with strain-gaug e plethysmography (SGP) was assessed in 425 patients referred to our v ascular laboratory because of clinically suspected deep-vein thrombosi s (DVT) of lower limbs, using venography as the reference standard. Th e inpatient/outpatient ratio was 236/189. Adequate venograms were obta ined in 401 patients and a DVT was diagnosed in 195 (49%). SGP results were borderline in 38 patients. In the 363 unequivocal cases, sensiti vity of SGP was 88% and specificity 90%. The sensitivity of D-dimer la tex test was 78% and the specificity 88%. Out of the 363 unequivocal c ases, D-dimer test results were discordant with SGP in 88 cases, of wh om 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 e rrors (false positive plus false negative results) from 10% (40/401; 9 5% 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% Cl, 7 -12%) to 31% (126/401; 95% CI, 27-36%). Most calf DVT (94%) were ident ified. We conclude that this test combination is valuable in the diagn osis of DVT in symptomatic patients, because of the high accuracy of c oncordant test results. Venography is required in case of borderline o r discordant results.