Out With the Old, in With the New: Age-Related D-Dimer Thresholds

Background: A fixed D-dimer cut-off threshold of 0.500 μg/mL is used in Blackrock Health Hermitage Clinic (BHHC) and most Haematology laboratories across Ireland, however, international guidelines have evolved over the past decade, and a growing body of evidence supports the use of age-adjusted D-dimer thresholds. This study evaluates the appropriateness of age-adjusted cut-offs in the patient population served by BHHC. Notably, inconsistent adherence to a formal hospital policy for the screening and diagnosis of venous thromboembolism (VTE) was observed throughout the clinical areas; the potential benefits of implementing such a policy are discussed herein. The integration of age-adjusted D-dimer thresholds with a validated clinical probability assessment tool may reduce unnecessary diagnostic imaging in patients investigated for VTE and prevent D-dimer testing in those deemed to have a ‘likely’ pre-test probability of VTE. Methods: A cross-sectional study was conducted to determine age-related D-dimer thresholds in a representative sample of patients attending BHHC. D-dimer measurements were performed using the ACL TOP 350 coagulation analyser with HemosIL D-dimer HS 500 reagents. Statistical analysis was carried out using IBM SPSS (v29) and Microsoft Excel. Ethical approval was obtained from the BHHC Clinical Governance Committee. Results: An age-related increase in D-dimer levels was observed. Applying an age-adjusted threshold (defined as patient age × 0.01 μg/mL for individuals aged 50 years and older) reduced false-positive results by 12.6% in this age group. Conclusion: Age-adjusted D-dimer thresholds are recommended, provided they are combined with a validated clinical probability assessment tool, such as the two-level Wells score. This approach improves diagnostic specificity and may reduce unnecessary imaging, particularly in older adults.