Evaluation of an ionized magnesium-pH analyzer--NOVA 8.
An ion-selective analyzer (NOVA 8 [previously NOVA CRT], NOVA Biomedical Waltham, USA) for simultaneous measurement of the concentration of ionized magnesium (cMG2+) and pH is investigated for linearity and influence of calcium ions on the Mg2+ results in different Mg2+ aqueous solutions with/without added calcium. Within the cMg2+ range 0-3.0 mmol/L, which covers most clinical values, we found cMg2+ values close to the line of identity, with a sensitivity about 94%, but 0.09 mmol/L lower in the absence of Ca2+. The analytical precision (CV) for human serum control was 1.7% in the physiological range. The accuracy and precision data for the Mg2+ electrode meet the demands for reliable results within the range for clinical use. We found a reference interval (95%) for cMg2+ of between 0.43 and 0.59 mmol/L serum, with a mean value of 0.51 mmol/L for healthy adults in the non-fasting state with no relation to sex or age. The mean cMg2+ was 61% of the mean concentration of plasma total magnesium (cTMg) ranging from (95%) 49% to 73%. No significant correlation was found between cMg2+ and total protein, albumin, phosphate, Ca2+, and total CO2. No significant difference was found between mean values for cMg2+ in whole blood, plasma, and serum. Serum samples could be stored for 24 h at 4 degrees C without significant change. Storage at -20 degrees C for 7 months caused a mean cMg2+ decrease of 8.3%. The mean slope delta lgcMg2+/delta pH measured after equilibration with different pCO2 values in each serum sample from the reference population was -0.0110, indicating a close agreement between the values for actual cMg2+ and adjusted cMg2+ (pH = 7.4).
Thode
J
J
Department Clinical Biochemistry, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark.
Juul-Jørgensen
B
B
Seibaek
M
M
Elming
H
H
Borresen
E
E
Jordal
R
R
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D002118:Calcium / Q000097:blood / Q000592:standards; D002245:Carbon Dioxide / Q000097:blood; D002412:Cations; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017736:Ion-Selective Electrodes; D016014:Linear Models; D008274:Magnesium / Q000097:blood* / Q000592:standards; D008297:Male; D008875:Middle Aged; D012015:Reference Standards; D012016:Reference Values; D015203:Reproducibility of Results
D002412:Cations; D002245:Carbon Dioxide; D008274:Magnesium; D002118:Calcium