| dc.description.abstract | With the invention o f the ion-selective electrode, ionic magnesium (iMg), the
biologically active form of Mg, is a common blood assay. There is some evidence that iMg
has considerable within subject variability. To further assess this, blood samples were
collected from 13 healthy volunteers 6X/day (7:00 - 22:00, every 3 hours) for 3 consecutive
days and analysed for iMg (NOVA Stat 8 Analyser). Individual ranges averaged .08 mmol/L
(range .05 to .14). Coefficients of variation (CV) ranged from 3% to 7% (mean 4%) while
analytical variation was determined to be 2.3%. Biological variability thus accounts for
almost half of the variability which is clinically significant as 9 of the 13 subjects recorded
at least one value below a reference range of .46 - .60 mmol/L. A significant within day
variation (p<.001) was noted, with differences between 7:00 and 10:00 as well as 10:00 and
22:00. Between day variations were not significant (p=.56). A plausible explanation of this
data is that iMg has a circadian rhythm, but a sinusoidal curve of best fit computed for each
subject did not correlate highly to iMg (r=.20). Thus, cautious interpretation of iMg values is
warranted until future research determines the nature of iMg variability. | |
