Contemporary diagnostic determination of D-dimer plasma concentration

Overview

There is currently no unified consensus regarding the units used for reporting laboratory results of D-dimers as a specific fibrin(ogen) degradation product (FDP). Within the professional community, there is ongoing discussion about which units should be used to report this marker of fibrin degradation, as well as which diagnostic assay should be applied, since different manufacturers use different measurement units. These includemg/L FEU andmg/L D-Dimer (DDU), each linked to different calibrators. We conducted a pilot comparative study of plasma D-dimer concentrations expressed in two commonly used units:mg/L FEU (fibrinogen equivalent units) andmg/L D-Dimer (DDU). The results were obtained using immunoturbidimetric measurement with two different diagnostic assays –⁠ one calibrated in mg/L D-Dimer and the other in mg/L FEU. Both D-dimer kits were provided by the same manufacturer and were based on the latex-enhanced immunoassay (LIA) principle using a highly sensitive method certified for the clinical exclusion of deep vein thrombosis (DVT) and pulmonary embolism (PE). A total of 65 plasma samples collected from adult patients (without stratification by sex, age, or diagnosis) were included in the study. D-dimer concentrations measured by both diagnostic assays were compared. The assay calibrated inmg/L D-Dimer was used as the primary routine method. The same plasma samples were subsequently analysed using the second diagnostic assay calibrated inmg/L FEU. The mean measured concentration was 0.524mg/L D-Dimer (SD = 1.066) and 1.598mg/L FEU (SD = 3.315). Statistical analysis using non-parametric Passing-Bablok regression demonstrated that the relationship between the two units is not simply twofold, as has sometimes been generally reported in the literature and assumed in clinical practice, but may in fact be up to threefold. Therefore, results obtained using different assays –⁠ i.e., without traceability to common calibrators, cannot be directly numerically compared. It is recommended to consistently use a single validated method with a manufacturer defined cut-off value.

Keywords:

Pulmonary embolism – D-dimers – disseminated intravascular coagulopathy – deep venous thrombosis – FEU (fibrinogen equivalent units) – fibrinolysis and fibrin degradation products – LIA (Latex Imuno Assay) – DDim (units:mg/l DDU)