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.