Commutability of reference materials for alkaline phosphatase measurements.

Commutability is a prerequisite when using a candidate reference materials (CanRMs) for calibration and trueness control of routine methods or for value transfer from the reference method to end-user calibrators of routine methods through a calibration hierarchy. The CanRMs include commercial general chemistry materials (GCs), enzyme trueness verification materials (ETVs), and secondary reference materials (SRMs). The commutability of CanRMs was evaluated based on the difference in bias and EP14-A3 to investigate their suitability for ALP measurement. A total of 44 fresh individual clinical samples (CSs) and the CanRMs were analyzed by six routine methods (validated methods) and by IFCC primary reference method (comparative method) for the determination of Alkaline Phosphatase (ALP). The commutability was performed based on IFCC working group recommendations for assessing commutability and analyzed according to EP14-A3 guide and difference in bias approach, respectively. The bias of the routine methods was assessed according to CLSI guidelines. The result of commutable materials obtained from the two evaluation approaches are not significantly different. It was observed that the routine methods with lower bias were associated with more commutable CanRMs. None of the CanRMs were suitable for use as commutable RMs. The findings of this study have a number of important implications for future practice.