Serum magnesium. A CAP survey--1975.

The results of the 1975 CAP Comprehensive Chemistry Survey of serum magnesium are presented. More than 1,260 laboratories participated in this survey. The most commonly used method for the measurement of serum magnesium concentrations is atomic absorption spectrophotometry. Colorimetric dye methods (Rapid-Stat (TM) kits, the Dupont ACA and titan yellow) follow in popularity. Variation in precision was lowest with atomic absorption and highest with titan yellow methods. All three of the dye-binding methods demonstrated either consistently negative or consistently positive biases when compared with the weighted mean concentration. The differences between the mean concentrations obtained by the dye-binding methods and atomic absorption spectrophotometry are statistically analyzed, and several conclusions are presented. As demonstrated by this survey and at the concentrations measured, the estimation of serum magnesium by any of the commonly used methods, except titan yellow, is clinically appropriate.