title: Clinically important intermethod differences for physiologically abnormal ionized magnesium results.
abstract: 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.
authors.affiliation: Clinical Pathology Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland 20892-1508, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Cecco
authors.forename: E N
authors.initials: EN
authors.lastname: Hristova
authors.forename: N N
authors.initials: NN
authors.lastname: Rehak
authors.forename: R J
authors.initials: RJ
authors.lastname: Elin
mesh_terms: D001774:Blood Chemical Analysis / Q000295:instrumentation* / Q000379:methods* / Q000592:standards; D002118:Calcium / Q000097:blood; D002623:Chemistry Techniques, Analytical / Q000295:instrumentation*; D004566:Electrodes; D004864:Equipment and Supplies; D006801:Humans; D008274:Magnesium / Q000097:blood*; D015203:Reproducibility of Results
chemical_list: D008274:Magnesium; D002118:Calcium