Estimation of precision and inaccuracy for serum magnesium determination on the basis of interlaboratory comparison data Accreditation ISO 15189.

Serum Mg is an important biochemical parameter in the context of clinical medicine for monitoring patients and for helping to diagnose some pathologies. The clinical laboratories must offer analytical results of quality in all parameters determined, demonstrating this way the laboratory "skill competence". The aim of this study was to revalidate (ISO 15189 standard) some different colorimetric methods for Mg determination in serum used in clinical and/or biochemical laboratories in four hospitals in Spain, on the basis of results of interlaboratory comparison programmes: Bio-Rad EQAS and external quality control SEQC. Precision and inaccuracy were estimated by analysis of records of an external quality control programme for Mg. The precision and inaccuracy values obtained were both less than 10%, except in one hospital in which the precision was less than 15%. These values of precision and inaccuracy obtained may be considered highly satisfactory taking into account the validation requirement for these ones: less than 10%. These findings demonstrate the effectiveness of the new revalidation methodology for diagnostic methods in medicine, which does not require any disruption of the laboratory's routine activity and which can be used even if the method in question has not been validated previously. It is also suggested that the ideas and requirements of ISO 15189 should be followed by the research laboratories.