FIGURE 2.

FT4 (top panel) and TSH (bottom panel) results for specimens from euthyroid subjects in the phase 1 and phase 2 studies: box plots of percentage differences. In the phase 2 study, manufacturers assayed a new panel of samples similar to the euthyroid specimens from the phase 1 study, using the conventional RMP mean results (for FT4) and the all-method mean values (for TSH) for the individual patients’ specimens to readjust their master calibrators, as would be required for implementation of standardization and harmonization. For phase 1 (left-hand plots), results are shown before and after mathematical recalibration as described in Figure 1. For phase 2 (right-hand plots), results are shown before and after manufacturers’ adjustment of their master calibrators. The dashed lines are drawn at arbitrary total error values of ±10%. FT4, free thyroxine; RMP, reference measurement procedure; TSH, thyroid-stimulating hormone. Adapted from reference 14 with permission.