To circumvent the problem of potential non commutability of calibrators in the reference measurement system, the C-STFT sees it as a conditio sine qua non to establish traceability by use of panels of commutable serum samples at the level of the “working calibrator” (14), (15). This implies that the panels, certified by a RMP or surrogate –, are used as working calibrator of the manufacturers’ master procedures (see Figure 1). In addition, the C-STFT uses the “Step-Up” design (16). It essentially comprises a sequence of method comparisons with selected sets of commutable samples (17) (fresh-frozen single donation samples, sourced by use of either the best available procedure for collecting high-volume blood donations (C37-A), or standard operating procedures commonly designed by routine laboratories). The design allows to decide after each step whether the step-up to the next phase can be made, or is premature. In the latter case the process can be stopped temporarily until sufficient progress has been made to pick up the standardization/harmonization activity later on. It allows to also investigate the intrinsic quality of the participating assays, more in particular, the analytical quality in terms of imprecision, within-run stability, between-run differences, calibration consistency etc.. It also lets document the assay consistency over time.