Age-Adjusted D-Dimer Cutoffs for DVT and Pulmonary Embolism: A Comparison of Five Assays

Background: Venous thromboembolism (VTE) is a common but underdiagnosed condition constituted primarily by deep venous thrombosis (DVT, 2/3) and pulmonary embolism (PE, 1/3).Diagnosis of VTE is based on the biomarker D-dimer for excluding low probability VTE, and imaging techniques to verify mid/high probability VTE. D-dimer assays generally have excellent sensitivity, but specificity is kept low by the physiology of the measurand. The plasma concentration of D-dimer increases in thrombosis and activated coagulation, but also in several other conditions such as pregnancy, cancer, trauma, inflammation, infection and with age. Many of these conditions are especially prevalent in VTE-patients, because they are also linked to an increased risk of venous thrombosis. Haase et al. showed that the plasma concentration of D-dimer in a healthy population increases with age, 50% of those ≥70 years old had a positive D-dimer (>0.5 mg/L FEU)1. Age-adjusted decision thresholds have subsequentially been recommended and validated, to increase specificity and reduce the rate of false positive D-dimer results in older patients without decreasing sensitivity. Aims: The study compares age-adjusted D-dimer decision thresholds for different assays in Swedish out-patients with suspected DVT or PE. Methods: Patients (n=940) with clinically suspected PE or DVT in a lower limb were recruited from the medical emergency department (ED) of Karolinska University Hospital, and fresh citrated plasma samples were analyzed for D-dimer within 30 minutes. D-dimer concentrations were measured by four immunoturbidimetric assays using the instruments Sysmex CS2100i and Stago CompactMax. VTE was verified by imaging techniques (ultrasonography, computed tomography or ventilation/perfusion lung scintigraphy, as appropriate) and classified into segmental or subsegmental PE and proximal or distal DVT. Non-VTE was identified by imaging techniques or absence of VTE in a three month follow up of medical records. Age adjusted cutoff values were calculated if age was ≥50 years according to Douma et al.2, as age x 0.01 for assays measured in mg/L FEU (Siemens INNOVANCE® D-dimer and STA®-Liatest® D-Di) and as age x 0.005 for Roche Tina-quant D-dimer and as age x 0.004 for MediRox D-dimer. Results: VTE was found in 125 patients (13.3%), PE in 35 (3.7%; 3.0% segmental and 0.7% subsegmental) and DVT in 90 (9.6%; 6.3% proximal and 3.4% distal). The diagnostic performances of the assays are displayed below, see