RELATIONSHIP BETWEEN IONIZED AND TOTAL MAGNESIUM IN SERUM

The relationship between the concentration of ionized magnesium and to tal magnesium was investigated. Ionized magnesium was determined by an ion-selective electrode (Microlyte 6, KONE) and the result was adjust ed to pH 7.4. Total magnesium concentration was measured by flame atom ic absorption spectrometry. Total and ionized magnesium were only clos ely related in marked hypermagnesaemia (> 1.2 mmol/L), but correlation was poor in samples with slightly elevated total concentration or in hypomagnesaemia (< 0.65 mmol/L). The relationship was dependent on pro tein concentration. The agreement between total and ionized magnesium was acceptable in normoproteinaemia, but in hypoproteinaemia (< 40 g/L ) total magnesium concentration was classified in 35% of the samples a s below or within the reference interval, whereas the pertinent ionize d magnesium concentration was normal or elevated, instead. Studies on paraproteinaemic sera clearly demonstrated that albumin concentration is most important for the size of the protein bound fraction.