Age-dependent D-dimer Cut-off Value Reduced Unnecessary Ultrasound Scans for Chinese Older Patients Suspected with Deep Vein Thrombosis

Objective: To evaluate whether the age-dependent D-dimer cut-off value would help to effectively decrease proportion of older patients suspected with deep vein thrombosis (DVT) to take unnecessary ultrasound imaging tests. Method: This prospective, single institution study was approved by the Institutional Ethics Committee of PLA General Hospital. The patients greater than 65 years with suspected DVT were enrolled in this study and underwent clinical estimations, D-dimer test and ultrasound scans of lower extremity. Clinical probability scores were graded as unlikely (score < 2 and likely (score≥2). Conventional cut-off value (500 μg/L) and age-dependent cut-off value (patient’s age × 10 μg/L) were applied for analyzing respectively. Evaluation and analysis include diagnostic accuracy (sensitivity and specificity), number of false negative results and 95% confidence intervals, and comparison of two cut-off values in different age groups. Results: A total of 1024 consecutive patients (76.4±19.3 years old) met the inclusion criteria. DVT was present in 256 patients (prevalence 25.0%). In 543 patients (Wells score < 2), DVT could be excluded in 193 patients using conventional cut-off value, while in 277 patients using age-dependent cut-off value, 84 patients could avoid unnecessary ultrasound scans. False negative rates were 3 patients (0.55%, 95% confidence interval 0.11-1.61%) using conventional cut-off vs. 4 patients (0.74%, 95% confidence interval 0.20-1.88%) using age-dependent cut-off value. The absolute increase in patients which DVT could be ruled out using the age-dependent cut-off value was largest in patients > 85 years.Conclusion: The age-dependent D-dimer cut-off value could help to exclude older patients with suspected DVT, to reduce unnecessary ultrasound scans, and to relieve the financial burden on patients, hospitals and society.