Clinical validation of an automated thin-film reflectance method for measurement of magnesium in serum and urine.

We evaluated an automated method for measuring total magnesium in serum, plasma, or urine that utilizes dry multilayered thin-film reagents and reflectance photometry for use on the Kodak Ektachem 400 analyzer. Comparison of magnesium results by this method and by atomic absorption revealed the following: the results on samples from a variety of patients agreed closely, the thin-film methodology was not affected by icteric, hemolyzed, or lipemic samples, and over 100 drugs studied did not interfere. Only very high concentrations of citrate and calcium affected magnesium results by this method. Both the accuracy and versatility of the thin-film method are well suited to routine, fast response, and pediatric testing in the clinical laboratory.