Sensitivity and Specificity of Instrumentation Lab Age-Adjusted D-Dimer Threshold Values in a Single Hospital Site: A Retrospective Analysis

Introduction The D-dimer is a common test in the assessment of chest pain in acute settings. With a high sensitivity and low specificity, a significant number of false positive outcomes occur, leading to unnecessary medical intervention. There is good evidence supporting the use of an age-adjusted D-dimer model to increase diagnostic specificity in the context of a conventional “D-dimer” assay. There is, however, a lack of evidence validating the age adjustment process when considering the less common but still widely utilized “instrumentation lab” assay. Methods A retrospective audit was carried out in a district general hospital by obtaining all acute computed tomography pulmonary angiograms carried out between December 2020 and August 2021. The age-adjusted D-dimer was calculated for each patient by multiplying the patient's age by 5. Thereafter, sensitivity and specificity were reassessed. Results After exclusion, 133 patients under 50 years of age with low pre-test probability scores were included in the analysis. Age-adjusted D-dimer was found to increase specificity from 2% to 28% whilst maintaining a sensitivity of 94%. Conclusion Utilization of the 5x age-adjusted instrumentation lab assay D-dimer results in increased specificity with the potential to reduce the number of unnecessary admissions, radiation exposure, and medication use, improving patient safety and reducing healthcare burden.