Review of Clinical Utility of Age-Adjusted D-Dimer Assay
Authors: Kelliher Sarah , Sharon Pearce , Melvin Breda , Maung Su Wai 
Published: November 2019

Background: Diagnosis of venous thromboembolism (VTE) uses biomarker D-dimer to exclude low probability VTE and imaging techniques to verify mid/high probability VTE. Plasma concentration of D-dimer increases with age in over 50 years and age-adjusted thresholds have been recommended and validated. Age-adjusted D-dimer reporting was introduced in Our Lady's Hospital (OLH) Navan in October 2018. By increasing the cut-off D-dimer values in older patients, a reduction in request for radiological investigations to out-rule VTE was anticipated.
Aims: To establish the clinical utility of using age-adjusted D-dimer reporting to our-rule VTE in clinical practice.
Methods: This retrospective analysis examined consecutive D-dimer results for individuals over age 50 during 5 months (May 2018 to September 2018) before and 5 months (October 2018 to February 2019) after introduction of age-adjusted D-dimer reporting. Data was collected from OLH Navan Laboratory information system and NIMIS (National Integrated Medical Imaging System).
Results: Five months prior to introduction of age-adjusted D-dimer reporting, 422 D-dimer tests were processed for patients over 50 years, of which 273(65%) were positive and 149(35%) were negative. In positive D-dimer group, 82 patients (30%) with positive results did not undergo radiological investigations. In remaining 191 patients with positive D-dimers, 21 patients (11%) had VTE (7 patients with Pulmonary Embolism (PE) and 4 patients with Deep Vein Thrombosis (DVT)). Over next 5 months following introduction of new D-dimer reporting, 290 D-dimer tests were performed for patients over 50 years, of which 65 (22%) had positive results and 225 (78%) had negative D-dimer. Five patients in positive group did not undergo further radiological tests. In the remaining 115 patients, 25 patients were diagnosed with VTE (22%), 4 patients with PE and 21 with DVT. Notably, 97 patients (33%) had negative D-dimer results that previously would have been positive with the old method. This resulted in reduction in request for number of radiological investigations. However, 20 individuals with negative age-adjusted D-dimer results had radiological investigations but reported negative for VTE. Only 15 patients in the negative group had results low enough that it would have been negative using non-age adjusted assay.
Conclusion: Proportion of patients with positive D-dimer results had significantly reduced using age-adjusted reporting. Total number of VTE cases was comparable between the two periods but diagnostic yield from radiological investigations increased from 11% to 22% following introduction of age-adjusted assay. Our audit did not reveal any VTE diagnosis being missed with new reporting method in negative D-dimer group. From our experience, clinical utility of D-dimer was enhanced following introduction of age-adjusted assay with subsequent increase in its specificity and reduction in radiological investigations requested to out-rule VTE. The new method also prevents patients from having unnecessary investigations with potential cost-saving benefits. The study did not find any evidence of compromising clinical efficacy in out-ruling VTE.

Disclosures
No relevant conflicts of interest to declare.