Magnesium fractions in serum of healthy individuals and CAPD patients, measured by an ion-selective electrode and ultrafiltration.
OBJECTIVE
Validation and comparison of a magnesium ion-selective electrode (ISE) with a cation-exchange resin technique, followed by determination of all magnesium fractions in serum of healthy volunteers and continuous ambulatory peritoneal dialysis (CAPD) patients.


METHODS
The analytical aspect has been studied by measuring the influence of complexing agents on the fraction ionized magnesium (friMg2+). A theoretical approximation of friMg2+, based on mass equilibria and complexation constants, was calculated and compared with the measurements.


RESULTS
ISE measurements showed good agreement with theory. Reference values of the ionized, protein-bound, and complexed magnesium fractions were (mean +/- SD) 0.65 +/- 0.04, 0.27 +/- 0.04, and 0.08 +/- 0.03, respectively. Fractions obtained in the CAPD group were 0.62 +/- 0.04, 0.22 +/- 0.05, and 0.16 +/- 0.05, respectively, and differed significantly from the values of the reference population.


CONCLUSIONS
All known serum magnesium parameters can be established by a combination of ultrafiltration, atomic absorption spectrometry, and ISE measurements. Unknown complexing compounds most probably account for the increased fraction of complexed magnesium in the serum of CAPD patients.
Huijgen
H J
HJ
Department of Clinical Chemistry, Academic Medical Centre, Amsterdam, The Netherlands.
van Ingen
H E
HE
Kok
W T
WT
Sanders
G T
GT
D000328:Adult; D000368:Aged; D002254:Carbonates / Q000737:chemistry; D002852:Chromatography, Ion Exchange / Q000379:methods; D002951:Citrates / Q000737:chemistry; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D017736:Ion-Selective Electrodes; D007676:Kidney Failure, Chronic / Q000097:blood / Q000378:metabolism*; D008274:Magnesium / Q000097:blood* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010531:Peritoneal Dialysis, Continuous Ambulatory; D010710:Phosphates / Q000737:chemistry; D012016:Reference Values; D014462:Ultrafiltration / Q000379:methods*
D002254:Carbonates; D002951:Citrates; D010710:Phosphates; D008274:Magnesium