title: Validation of an enzymatic total magnesium determination based on activation of modified isocitrate dehydrogenase.
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.
authors.affiliation: Department of Clinical Biochemistry, the Royal London School of Medicine and Dentistry, London, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Stone
authors.forename: P E
authors.initials: PE
authors.lastname: Chowdrey
authors.forename: P
authors.initials: P
authors.lastname: Miall
authors.forename: C P
authors.initials: CP
authors.lastname: Price
mesh_terms: D001391:Azo Compounds; D002951:Citrates; D019343:Citric Acid; D004789:Enzyme Activation; D005470:Fluorometry; D006801:Humans; D007521:Isocitrate Dehydrogenase / Q000097:blood*; D008274:Magnesium / Q000097:blood*; D009249:NADP; D013054:Spectrophotometry, Atomic
chemical_list: D001391:Azo Compounds; D002951:Citrates; C040875:xylidyl blue I; D019343:Citric Acid; D009249:NADP; D007521:Isocitrate Dehydrogenase; D008274:Magnesium