REFERENCE INTERVAL FOR WHOLE-BLOOD IONIZED MAGNESIUM IN A HEALTHY POPULATION AND THE STABILITY OF IONIZED MAGNESIUM UNDER VARIED LABORATORYCONDITIONS

Objective: To establish a reference interval for ionized magnesium (iM g), to evaluate the stability of whole blood iMg under varied laborato ry storage conditions, and to study the correlation between total and iMg in healthy Volunteers and in an intensive care unit (ICU) populati on. Methods: Blood specimens were collected anaerobically from 125 hea lthy volunteers and 200 ICU patients into tubes containing lithium hep arin, transported to the laboratory on ice, stored at 4 degrees C and analyzed within 2 h on a NOVA 8 Electrolyte Analyzer. Additional speci mens were stored under different conditions before analysis to assess the stability of iMg. Results: In healthy volunteers, the mean whole b lood iMg level was 0.52 mmol/L with a range of 0.44 to 0.59 mmol/L. Th e iMg/total serum Mg ratio was at 0.60 (0.50-0.69). Regression analysi s of iMg vs total Mg produced a correlation coefficient (r) of 0.48 (p < 0.0001). lonized Mg levels were comparable between males and female s (0.52 +/- 0.04 vs 0.51 +/- 0.03, p = 0.38). In the ICU group, a wide r range of iMg results was observed (0.35-0.78 mmol/L) and the correla tion between iMg and total Mg was r = 0.71 (p < 0.0001). storage of wh ole blood specimens in uncapped tubes at room temperature resulted in a small, but significant, decrease in iMg over a 6-h period. Little ch ange was seen in capped tubes stored either at room temperature or at 4 degrees C, over 6 h, or at 4 degrees C over 5 days. Conclusions: Usi ng the NOVA 8 Electrolyte Analyzer, we established a reference interva l for whole blood iMg in a healthy Canadian population. The correlatio n between ionized Mg and total Mg was weak, but statistically signific ant. lonized Mg levels in lithium heparin tubes were stable over 5 day s when specimens were stored at 4 degrees C, suggesting that specimens may be stored at least overnight prior to processing.