Use of different d‐dimer levels to exclude venous thromboembolism depending on clinical pretest probability

Summary.  Currently, the same d‐dimer cut‐off point is used to define a positive result for all patients with suspected venous thromboembolism, regardless of their pretest probability. However, use of a relatively high d‐dimer cut‐off point (lower sensitivity) for those with a low clinical pretest probability, and a low d‐dimer cut‐off point (higher sensitivity) for those with a high clinical pretest probability, may be preferable. To determine if using three different d‐dimer cut‐off points according to low, moderate or high clinical pretest probability has greater utility for exclusion of venous thromboembolism than using the same single d‐dimer cut‐off point in all patients. Data from a previously published study of 571 patients was used to identify the highest d‐dimer cut‐off point with a negative predictive value of at least 98% for the subgroup of patients with low and high pretest probability. The d‐dimer cut‐off point for those with moderate clinical pretest probability remained unchanged [0.5 fibrinogen equivalent units (FEU) µg mL−1]. Accuracy of d‐dimer testing for venous thromboembolism using three cut‐off points vs. one cut‐off point was than determined. d‐dimer cut‐off points of 0.2 and 2.1 FEU µg mL−1 were selected for the high and low pretest probability groups, respectively. When three pretest probability‐specific cut‐off points were used instead of the previously determined single d‐dimer cut‐off point (0.5 FEU µg mL−1), sensitivity and negative predictive value were unchanged (95 and 98%, respectively), but specificity increased from 44.7 to 60.4% (P < 0.001). This resulted in exclusion of venous thromboembolism in 80 additional patients. Use of three pretest probability‐specific d‐dimer cut‐off points rather than a single d‐dimer cut‐off point for all patients, has the potential to increase the utility of d‐dimer testing for the diagnosis of venous thromboembolism.