Comparing D-dimer assays

• Including many patients with elevated D-dimer concentrations due to other causes than VTE may give a false increase in sensitivity and negative predictive value • The prevalence of VTE has an influence on the predictive values – higher prevalence gives lower NPV • A high ratio of proximal to distal DVT will increase both the sensitivity and the negative predictive value • A study focused on PE will have a higher sensitivity and negative predictive value compared to a study including DVT without PE • Changing cut-off will change clinical sensitivity and specificity • When ultrasound is used as the “gold standard”/ confirmatory method, the sensitivity and negative predictive value are falsely increased compared to when venography/angiography is used • When all the persons in the tested population are not examined by a confirmatory method, falsely increased clinical sensitivity and negative predictive value may be seen