title: Analyzer-dependent differences in results for ionized calcium, ionized magnesium, sodium, and pH.
abstract: We compared two ion-selective analyzers (AVL 988-4 and NOVA CRT) for determining ionized calcium (iCa2+), ionized magnesium (iMg2+), sodium (Na+), and pH in serum specimens from healthy and diseased individuals. For assays of three levels of protein-based control materials, total imprecision (CV) was < 3% for all analytes except iMg2+ (< or = 6.5% on NOVA, and < or = 4.9% on AVL). We found a significant difference between the analyzers (P < 0.001) for the mean iMg2+ concentration in patients but no significant correlation (r = 0.253) between the analyzers for iMg2+ in specimens from healthy volunteers, even though the mean iMg2+ concentration did not differ significantly between these groups. The reference interval (central 95 percentiles) for iMg2+ with AVL (0.44-0.60 mmol/L) was contained within that of NOVA (0.39-0.64 mmol/L). The AVL gave higher values for iCa2+ (P < 0.001) and lower values for pH (P < 0.001) in specimens from normal volunteers and patients. The mean value for Na+ in patients' samples was significantly higher by the NOVA (P < 0.01) than by the AVL analyzer. Thus, we found significant differences between these two analyzers for all four analytes.
authors.affiliation: Clinical Pathology Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: E N
authors.initials: EN
authors.lastname: Hristova
authors.forename: S
authors.initials: S
authors.lastname: Cecco
authors.forename: J E
authors.initials: JE
authors.lastname: Niemela
authors.forename: N N
authors.initials: NN
authors.lastname: Rehak
authors.forename: R J
authors.initials: RJ
authors.lastname: Elin
mesh_terms: D002118:Calcium / Q000097:blood*; D002412:Cations; D004566:Electrodes / Q000592:standards; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000097:blood*; D011199:Potentiometry / Q000295:instrumentation / Q000706:statistics & numerical data*; D012016:Reference Values; D012680:Sensitivity and Specificity; D012964:Sodium / Q000097:blood*
chemical_list: D002412:Cations; D012964:Sodium; D008274:Magnesium; D002118:Calcium