Fig. 2. Structure of a calibration hierarchy whereby patient results are traceable to higher order reference materials such as World Health Organisation (WHO) International Standard materials, through a series of linked calibrations.

An example of this is in the standardization of BCR::ABL1/reference gene ratio to the International Scale. Modified from ISO 17511:2020 Figure 4 model calibration hierarchy for “international conventional calibrator” that defines the quantity intended to be measured (“measurand”) [15]. IVD, in vitro diagnostic medical device. Created with BioRender.com.