Age‐adjusted D‐dimer, clinical pre‐test probability‐adjusted D‐dimer, and whole leg ultrasound in ruling out suspected proximal and calf deep venous thrombosis

D‐dimer (DD) and ultrasonography (US) are part of the diagnostic workup for lower‐extremity deep vein thrombosis (DVT). Recent studies have shown that adjusting DD level cut‐offs by age or clinical pre‐test probability (PTP) decreases the use of US. We compared diagnostic accuracy of PTP‐adjusted DD and age‐adjusted DD in 3883 patients (F: 61.1%; age: 65.3 ± 16.8 y) referred to our unit for clinically suspected DVT. All patients underwent clinical evaluation, DD, and US. Proximal DVT was detected in 477 (12.4%) patients, and distal DVT was isolated in 342 (8.9%) patients. In the remaining 3064 patients there were 23 venous thromboembolic events (0.75%, 95% CI: 0.50–1.12) during the 3‐month follow‐up. The specificities of DD, age‐adjusted DD, and PTP‐adjusted DD in patients without high PTP levels were 47% (95% CI: 45–49), 61% (95% CI: 59–62), and 67% (95% CI: 65–68), respectively. The negative predictive value (NPV) was 96% (95% CI: 95–97) for all diagnostic strategies. When only proximal DVTs were considered, the NPV increased to 99% (95% CI: 98–99). US was avoided in 37% (95% CI: 36–38) of patients with a fixed cut‐off DD, 48% (95% CI: 47–50) with age‐adjusted DD, and 52% (95% CI: 51–54) with PTP‐adjusted DD. The failure rate for all DVTs of DD, age‐adjusted DD, and PTP‐adjusted DD was 2.0% (95% CI: 1.6–2.5), 2.7% (95% CI: 2.2–3.2), and 2.5% (95% CI: 2.1–3.0), respectively. Compared with the standard DD cut‐off, both age‐adjusted and PTP‐adjusted DD reduced the proportion of patients who required US at the cost of a small increase in failure rate.