Evaluation of intrinsic and routine quality of serum total magnesium measurement

We investigated the intrinsic (as delivered by the manufacturer) and routin e quality of four systems for measurement of serum total magnesium (t-Mg2+) by method comparison with an ion chromatography reference method. The resu lts of the study were interpreted on the basis of analytical quality specif ications derived from the biological variation of t-Mg2+, expanded by the a nalytical uncertainty of the reference measurements. This resulted in limit s for systematic error of 2.1% and for total error of 4.3%. The study demon strated that those limits were challenging for all routine systems. Most of them met the total error criterium just borderline and one showed a consid erable systematic error (-5.2%). Concerning the measurement quality in the routine laboratories, the study showed that many were unable to preserve th e intrinsic quality of the respective manufacturer. Consequently, loss of s ystem performance in the routine laboratory mostly led to violation of the analytical specifications. Most strikingly, the study revealed enormous qua lity differences between routine laboratories, This indicates that, still, many routine laboratories do not make adequate use of currently available i nternal and external quality control tools. Moreover, some laboratories con siderably expanded the high end of the reference interval, thereby reducing the diagnostic potential of t-Mg2+. (C) 2000 Elsevier Science B.V. All rig hts reserved.