Clinically important intermethod differences for physiologically abnormal ionized magnesium results

• Published in: American journal of clinical pathology Vol. 108; no. 5; pp. 564 - 569
• Main Authors: CECCO, S. A, HRISTOVA, E. N, REHAK, N. N, ELIN, R. J
• Format: Journal Article
• Language: English
• Published: Chicago, IL American Society of Clinical Pathologists 01.11.1997
• Subjects: Biological and medical sciences; Blood Chemical Analysis - instrumentation; Blood Chemical Analysis - methods; Blood Chemical Analysis - standards; Calcium - blood; Chemistry Techniques, Analytical - instrumentation; Electrodes; Equipment and Supplies; Humans; Investigative techniques, diagnostic techniques (general aspects); Magnesium - blood; Medical sciences; Miscellaneous. Technology; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Reproducibility of Results; Assay; Human; Electrolyte; Ionization; Automatic analyzer; Serum; Magnesium; Technique; Comparative study
• ISSN: 0002-9173; 1943-7722
• DOI: 10.1093/ajcp/108.5.564

We compared physiologically abnormal low and high ionized magnesium (iMg) results determined with the AVL 988-4 (AVL, Graz, Austria) and Nova CRT (Nova Biomedical, Waltham, Mass) ion-selective electrodes (ISEs) in serum samples from randomly selected patients. A result of < 0.39 mmol/L with either ISE constituted the low magnesium group and of > or = 0.65 mmol/L the high magnesium group. Within each group we found significant differences between the iMg results. Major intermethod differences were found for samples with physiologically normal total magnesium concentration: most of the samples in the low magnesium group (83%) had abnormally low results with the Nova ISE, whereas most of the results with the AVL ISE (83%) were normal. In contrast, all results with the AVL ISE for the high magnesium group were abnormally high, but 67% of the results with the Nova ISE were normal. The agreement for the clinical interpretation of iMg results based on the reference interval for each method was only 32%. The differences in iMg results between the two analyzers must be resolved before using the iMg test as measured with ISE for patient care.