Optimal D-Dimer Cutoff Values for Diagnosing Deep Vein Thrombosis in Patients with Comorbid Malignancies

Background: Patients with malignancy are at high risk of venous thromboembolism, and early diagnosis is important. The Khorana score is known as a risk assessment for cancer-related thrombosis during chemotherapy, but there are still few reports on its diagnostic potential, the optimal D-dimer cutoff values for indications other than chemotherapy and the use of the Khorana score in combination with D-dimers. In this study, we examined the clinical appropriateness of increasing the D-dimer cutoff value.Methods: We retrospectively studied 208 malignancies out of 556 patients who underwent lower extremity venous ultrasonography at our hospital over a 2-year period from January 2018 to December 2019. The optimal D-dimer cutoff value for predicting deep vein thrombosis (DVT) in patients with malignancy was calculated by the Youden index. The usefulness of the Khorana score alone and the model combining the Khorana score with D-dimer for predicting DVT diagnosis was compared using receiver operating characteristic analysis.Results: Of 208 eligible patients, 59 (28.4%) had confirmed DVT. The optimal D-dimer cutoff value for predicting DVT comorbidity in patients with malignancy was 3.96 mg/mL. When the new D-dimer cutoff value was set at 4.0 mg/mL, the odds ratio (OR) for DVT diagnosis was 4.23 (95% confidence interval (CI) 2.10-8.55, P < 0.001), which was higher than the OR of 1.33 (95% CI: 0.98-1.81, P = 0.064) for the Khorana score. The area under the curve for the Khorana score and D-dimer was 0.714, which was significantly higher than the 0.611 for the Khorana score alone, with the difference being significantly higher at 0.103 (P = 0.004, 95% CI: 0.033-0.173).Conclusions: The optimal D-dimer cutoff value for the diagnosis of DVT in patients with malignancy was 4.0 mg/mL. It was also suggested that the combination of the Khorana score with the D-dimer level was more accurate in diagnosing DVT than the Khorana score alone.