Combination of pretest clinical probability score and different (pp. 59-72)
Authors: (Takashi Yamaki)
Abstract: Prompt diagnosis of venous deep vein thromboembolism (VTE) is mandatory, but only 25% of suspected cases are confirmed by objective testing. In this background, the D-dimer testing with high negative predictive value represents an excellent triage test in patients with suspected VTE. In general, enzyme-liked immunosorbent assay (ELISA) offers the best of current D-dimer assay for sensitivity. Latex quantitative assay and whole-blood assay might also represent valid alternative for
exclusion of VTE. Recently, a combination of pretest clinical probability (PTP) score and D-dimer testing has been considered validated as a diagnostic strategy for pulmonary embolism or deep vein thrombosis (DVT). This strategy is specifically validated for patients who have low PTP. Even the combination of low PTP and a normal D-dimer concentration can be considered a safe strategy to withhold anticoagulation in patients with suspected VTE.
D-dimer cutoff value also affects the discriminating power. The sensitivity could be improved by lowering the cutoff value, but the subsequent decrease in specificity would lead to a large number of false-positive results. On the contrary, D-dimer assays with very high specificity provide fewer false-positive results, but they are less sensitive for VTE and cannot be used to exclude the disease in all patients. In this background, we analyzed if varying the D-dimer cutoff according to PTP would exclude VTE in more patients than using the single D-dimer cutoff point. Using latex agglutination assay, we found that D-dimer cutoff points of 2.6, 1.1 and 1.1μg/mL were selected for the low, moderate and high PTP groups among 886 patients with suspected DVT. In the low PTP group, specificity increased from 48.9% to 78.2% (P <0.0001) 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. Regardless, overall venous duplex scanning could have been reduced by 43.0% using different D-dimer cutoff points. Even in patients with proven PE, a combination of a specific D-dimer level and PTP score is most effective in the low PTP patients in excluding DVT.
In summary, a combination of PTP score and different D-dimer cutoff provides an effective means in terms of avoiding a large number of unnecessary venous duplex scanning in suspected symptomatic DVT in the low PTP for DVT.