Serum ionized versus total magnesium in patients with chronic renal disease.
BACKGROUND
Recent technology has made it possible to assess serum ionized magnesium with user-friendly ion-selective electrodes similar to measurement of the serum calcium concentration.


METHODS
We measured the serum ionized (Mg2+) and total magnesium (tMg) concentration in 69 patients with chronic kidney disease (38 men, 31 women, age 22-85 years) and in 75 control subjects.


RESULTS
In control subjects the reference ranges were as follows: serum Mg2+ 0. 45-0.67 mmol/l, and tMg 0.67-0.96 mmol/l. In patients with chronic renal failure serum Mg2+ was 0.57 +/- 0.05 mmol/l and tMg 0.80 +/- 0. 11 mmol/l, and in transplant recipients receiving cyclosporine 0.53 +/- 0.05 and 0.71 +/- 0.10 mmol/l, respectively. The correlation coefficient between serum Mg2+ and tMg was r = 0.73 (p < 0.001) in the patient group and r = 0.75 (p<0.001) in control subjects. Serum tMg was below the reference range in 15 of 69 measurements. However, serum Mg2+ was below the reference range in only 1 of these 15 samples. Hence, 14 of 69 cases with low tMg but normal Mg2+ were false-positive with respect to hypomagnesemia.


CONCLUSIONS
We conclude that tMg may overestimate the incidence of hypomagnesemia, and the measurement of Mg2+ may be of benefit when studying patients with expected hypomagnesemia.
Saha
H
H
Department of Medicine, University of Tampere Medical School, Tampere University Hospital, Tampere, Finland. llhesa@uta.fi
Harmoinen
A
A
Nisula
M
M
Pasternack
A
A
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002412:Cations; D002908:Chronic Disease; D005260:Female; D006801:Humans; D007674:Kidney Diseases / Q000097:blood*; D008274:Magnesium / Q000097:blood*; D008297:Male; D008875:Middle Aged
D002412:Cations; D008274:Magnesium