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Falsely high ionized magnesium results by an ion-selective electrode method in severe hypomagnesemia.
Eur J Clin Chem Clin Biochem 1997; 35(9):701-9EJ

Abstract

Changes in serum total and ionized magnesium (Mg and Mg2+) and calcium (Ca and Ca2+) were monitored in three patients who transiently developed severe (total Mg < 0.50 mmol/l) to profound hypomagnesemia (total Mg < 0.35 mmol/l) due to cisplatin or interleukin-2 therapies. Mg2+ and Ca2+ were measured with the Nova ion-selective electrodes at 37 degrees C and all results were normalized to pH 7.40. Independent of the etiology, the Mg2+ fraction (Mg2+/total Mg) increased as the concentration of the serum total Mg decreased in all three patients. When the total Mg was around or below 0.35 mmol/l the Mg2+ approached or exceeded total Mg, suggesting an error in the measurement of Mg2+. The findings were extended by including a group of 31 additional patients whose serum total Mg, Mg2+, total Ca, and Ca2+ concentrations varied from abnormally low to above normal. The serum total and ionized concentrations strongly correlated for both Mg (r2 = 0.88) and Ca (r2 = 0.92). The Mg2+ fraction rapidly increased with a fall in the total Mg concentration (r2 = 0.76) and total Mg/total Ca ratio (r2 = 0.71). In fact, with decreasing total Mg concentrations or total Mg/total Ca ratios, the Mg2+ fraction progressively increased to 93-128% of the total, confirming an error in the Mg2+ determinations. The Ca2+ fraction showed a slight and insignificant decrease with falling total Ca concentrations and total Mg/total Ca ratios. The Mg2+ concentration was directly related (r2 = 0.62), whereas the Ca2+ concentration showed a complex relationship to the total Mg/total Ca ratio. Whether this latter relationship represents a technical artifact or a true biological phenomenon requires further study. The apparent overestimation of Mg2+ at very low total Mg concentrations, and in the presence of a very low total Mg/total Ca ratio, could be due to improper chemometric correction of the Ca effect on the Mg electrode, non-linearity, and inadequate calibration. Whatever the mechanism, the failure of this method to correctly measure very low serum Mg2+ concentrations in the sera of patients with severe hypomagnesemia, or likely in any patient with an unusually low total Mg/total Ca ratio, erodes its diagnostic usefulness.

Authors+Show Affiliations

Clinical Pathology Department, W. G. Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland, USA. gcsako@nih.govNo affiliation info availableNo affiliation info available

Pub Type(s)

Case Reports
Journal Article

Language

eng

PubMed ID

9352233

Citation

Csako, G, et al. "Falsely High Ionized Magnesium Results By an Ion-selective Electrode Method in Severe Hypomagnesemia." European Journal of Clinical Chemistry and Clinical Biochemistry : Journal of the Forum of European Clinical Chemistry Societies, vol. 35, no. 9, 1997, pp. 701-9.
Csako G, Rehak NN, Elin RJ. Falsely high ionized magnesium results by an ion-selective electrode method in severe hypomagnesemia. Eur J Clin Chem Clin Biochem. 1997;35(9):701-9.
Csako, G., Rehak, N. N., & Elin, R. J. (1997). Falsely high ionized magnesium results by an ion-selective electrode method in severe hypomagnesemia. European Journal of Clinical Chemistry and Clinical Biochemistry : Journal of the Forum of European Clinical Chemistry Societies, 35(9), pp. 701-9.
Csako G, Rehak NN, Elin RJ. Falsely High Ionized Magnesium Results By an Ion-selective Electrode Method in Severe Hypomagnesemia. Eur J Clin Chem Clin Biochem. 1997;35(9):701-9. PubMed PMID: 9352233.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Falsely high ionized magnesium results by an ion-selective electrode method in severe hypomagnesemia. AU - Csako,G, AU - Rehak,N N, AU - Elin,R J, PY - 1997/11/14/pubmed PY - 1997/11/14/medline PY - 1997/11/14/entrez SP - 701 EP - 9 JF - European journal of clinical chemistry and clinical biochemistry : journal of the Forum of European Clinical Chemistry Societies JO - Eur J Clin Chem Clin Biochem VL - 35 IS - 9 N2 - Changes in serum total and ionized magnesium (Mg and Mg2+) and calcium (Ca and Ca2+) were monitored in three patients who transiently developed severe (total Mg < 0.50 mmol/l) to profound hypomagnesemia (total Mg < 0.35 mmol/l) due to cisplatin or interleukin-2 therapies. Mg2+ and Ca2+ were measured with the Nova ion-selective electrodes at 37 degrees C and all results were normalized to pH 7.40. Independent of the etiology, the Mg2+ fraction (Mg2+/total Mg) increased as the concentration of the serum total Mg decreased in all three patients. When the total Mg was around or below 0.35 mmol/l the Mg2+ approached or exceeded total Mg, suggesting an error in the measurement of Mg2+. The findings were extended by including a group of 31 additional patients whose serum total Mg, Mg2+, total Ca, and Ca2+ concentrations varied from abnormally low to above normal. The serum total and ionized concentrations strongly correlated for both Mg (r2 = 0.88) and Ca (r2 = 0.92). The Mg2+ fraction rapidly increased with a fall in the total Mg concentration (r2 = 0.76) and total Mg/total Ca ratio (r2 = 0.71). In fact, with decreasing total Mg concentrations or total Mg/total Ca ratios, the Mg2+ fraction progressively increased to 93-128% of the total, confirming an error in the Mg2+ determinations. The Ca2+ fraction showed a slight and insignificant decrease with falling total Ca concentrations and total Mg/total Ca ratios. The Mg2+ concentration was directly related (r2 = 0.62), whereas the Ca2+ concentration showed a complex relationship to the total Mg/total Ca ratio. Whether this latter relationship represents a technical artifact or a true biological phenomenon requires further study. The apparent overestimation of Mg2+ at very low total Mg concentrations, and in the presence of a very low total Mg/total Ca ratio, could be due to improper chemometric correction of the Ca effect on the Mg electrode, non-linearity, and inadequate calibration. Whatever the mechanism, the failure of this method to correctly measure very low serum Mg2+ concentrations in the sera of patients with severe hypomagnesemia, or likely in any patient with an unusually low total Mg/total Ca ratio, erodes its diagnostic usefulness. SN - 0939-4974 UR - https://www.unboundmedicine.com/medline/citation/9352233/Falsely_high_ionized_magnesium_results_by_an_ion_selective_electrode_method_in_severe_hypomagnesemia_ DB - PRIME DP - Unbound Medicine ER -