Currently, the latex agglutination D-dimer assay is widely used for excluding deep
vein thrombosis (DVT) but is considered less sensitive than the enzyme-linked immunosorbent
assay-based D-dimer test. The purpose of the present study was to determine if a combination
of different cutoff points, rather than a single cutoff point of 1.0 microg/mL, on
the latex agglutination D-dimer assay and the pretest clinical probability (PTP) score
would be able to reduce the use of venous duplex ultrasound (DU) scanning in patients
with suspected DVT.
The PTP score and D-dimer testing were used to evaluate 989 consecutive patients with
suspected DVT before venous DU scanning. After calculating the clinical probability
scores, patients were divided into low-risk (< or =0 points), moderate-risk (1-2 points),
and high-risk (> or =3 points) pretest clinical probability groups. Receiver operating
characteristic (ROC) curve analysis was used to determine the appropriate D-dimer
cutoff point for each PTP with a negative predictive value of >98% for a positive
DU scan.
There were 886 patients enrolled. The study group included 609 inpatients (68.7%)
and 277 outpatients (31.3%). The prevalence of DVT in this series was 28.9%. There
were 508 patients (57.3%) classified as low-risk, 237 (26.8%) as moderate-risk, and
141 (14.9%) as high-risk PTP. DVT was identified in 29 patients (5.7%) with low-risk,
118 (49.8%) with moderate-risk, and 109 (77.3%) with high-risk PTP scores. ROC curve
analysis was used to select D-dimer cutoff points of 2.6, 1.1, and 1.1 microg/mL for
the low-, moderate- and high-risk PTP groups, respectively. In the low-risk PTP group,
specificity increased from 48.9% to 78.2% (P < .0001) with use of the different D-dimer
cutoff value. In the moderate- and high-risk PTP groups, however, the different D-dimer
levels did not achieve substantial improvement. Despite this, the overall use of venous
DU scanning could have been reduced by 43.0% (381 of 886) if the different D-dimer
cutoff points had been used.
Combination of a specific D-dimer level with the clinical probability score is most
effective in low-risk PTP patients for excluding DVT. In moderate- and high-risk PTP
patients, however, the recommended cutoff points of 1.0 microg/mL may be preferable.
These results show that different D-dimer levels for patients differing in risk is
feasible for excluding DVT using the latex agglutination D-dimer assay.