Validation of an enzymatic total magnesium determination based on activation of modified isocitrate dehydrogenase.

M J Stone, P E Chowdrey, P Miall, C P Price

Index: Clin. Chem. 42(9) , 1474-7, (1996)

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Abstract

We have evaluated an enzymatic assay for the determination of Mg in serum, based on the activation of a chemically modified form of isocitrate dehydrogenase by Mg2+. In the presence of potassium isocitrate and NADP+, NADPH, which absorbs light at 340 nm, is produced, and its increase is proportional to Mg2+ in the sample. We have shown linearity to at least 5 mmol/L Mg and good precision by within-run CVs between 1.4% and 3.5% and day to day CVs between 3.2% and 5.4%. The method (y) is accurate, comparing well with the xylidyl blue method (x), with a Deming regression of y = 0.930x - 0.063 (r = 0.98, S(y/x) = 0.019), and with atomic absorption spectrophotometry (x), with a Deming regression of y = 0.932x - 0.016 (r = 0.97, S(y/x) = 0.023), and shows no interference from common endogenous compounds in blood and various metal ions except for visibly hemolyzed samples. A rapid assay, with reagents that are stable for at least 30 days at 4 degrees C and requiring no prior preparation, it is simple to use and suitable for adaptation onto automated chemistry analyzers.