Discordant D-dimer results of two rapid quantitative automated assays are related to age

Using an age and fibrinogen levels adjusted D-dimer cutoff significantly improves the specificity of two equivalent D-dimer assays for excluding pulmonary embolism

OBJECTIVES

Our single-center prospective study compared two methods of D-dimer determination used in the exclusion of pulmonary embolism: bioMérieux method, VIDAS® D-Dimer Exclusion™ II, and Diagnostica Stago method, STA®-Liatest® D-Di Plus. For each of these two methods, we calculated optimized variable cutoffs based on fibrinogen and/or age to improve the specificity of the methods.

PATIENTS - METHODS

2530 patients admitted to the Emergency Department of the Brest University Hospital for suspected pulmonary embolism were included in this study. The comparison of the two methods was performed by calculating their different characteristics: sensitivity, specificity and negative predictive value for different cutoffs systems: fixed or age-adjusted according to Douma et al. An optimization of the variable cutoff according to age and fibrinogen was then performed.

RESULTS

The two methods VIDAS and STAGO are approximately equivalent in terms of performance even if the STAGO method presents a better specificity (57.1 %) at the fixed cutoff of 0.5 μg/mL. The adoption of age-adjusted, fibrinogen-adjusted or doubly-adjusted (age and fibrinogen) cutoffs, significantly improves the specificity of the tests without affecting their excellent sensitivity. These specificities peak respectively at 75.8 % and 76 % for the VIDAS and STAGO tests when using a doubly-adjusted, age and fibrinogen, cutoff, i.e. a gain in specificity of approximately 10 % compared with the age-adjusted cutoff of Douma et al. and of approximately 20 % compared with the fixed cutoff of 0.5 μg/mL.

CONCLUSION

Adopting an optimized variable cutoff based on fibrinogen and/or age significantly improves specificity of D-dimer methods for pulmonary embolism exclusion.

Comparison of five D-dimer reagents and application of an age-adjusted cut-off for the diagnosis of venous thromboembolism in emergency department

There is still a considerable uncertainty concerning D-dimer cut-off values used in exclusion of venous thromboembolic (venous thromboembolism, VTE) disease, especially among the elderly patients. The objectives were to compare five different D-dimer reagents in the daily practice of an emergency department and to test retrospectively the performances of an age-adjusted cut-off. A total of 473 consecutive ambulatory outpatients suspected of VTE (confirmed VTE = 21) were included in this study. Five commercially available tests were assessed: STA-Liatest D-Di (LI), AxSYMD-Dimer (AX), VIDAS D-Dimer (VI), INNOVANCE D-Dimer (IN), and HemosIL D-Dimer HS (HS). When using a cut-off value of 500 ng/ml fibrinogen equivalent units (FEUs), D-dimer reagents differ in their abilities to avoid further testing. Indeed, LI allowed exclusion of VTE diagnosis in statistically more patients than VI, AX, and IN but not HS. The use of an age-adjusted cut-off is cost-effective without increasing significantly the number of false negative results. The interest of such strategy is more or less pronounced, depending on the type of D-dimer reagent. The application of an age-adjusted cut-off may be useful to reduce differences among D-dimer reagents to lower costly imaging studies. Prospective validation studies on large cohorts of patients are required to determine the safety of such strategy.