Harmonization of fibrinogen assay results: study within the framework of the Dutch project 'Calibration 2000'

In a Dutch project for harmonization of fibrinogen assays, the commutability of potential calibrators for fibrinogen was assessed by means of a twin-study design, which is, in essence, a multicentre, split-patient sample, between-field-methods protocol. The study consisted of simultaneous analysis of fresh-frozen patient plasmas and three potential calibrators for fibrinogen by 48 Dutch laboratories forming 24 couples. The state-of-the-art intralaboratory standard deviation was used to assess the commutability of the potential calibrators. The potential calibrators were commutable for the Clauss, but not for the prothrombin time (PT)-derived assays. One potential calibrator was used in an attempt to harmonize fibrinogen assay results in a Dutch field study. The interlaboratory coefficient of variation (CV) of three out of four test samples could be reduced significantly using the common calibrator. The average overall CV for the four test samples was 10.3% using the routine measurements and 7.8% using the common calibrator. Despite the reduction in the overall CV, the bias between Clauss and PT-derived assay results in two coumarin test samples could not be eliminated.