Using capillary zone electrophoresis, the urine creatinine (uCr) assay was
validated in extemporaneous diluted urine, both in healthy subjects and ath
letes, with the uCr concentration as a reference value to compare excretion
rates of other metabolites in the same samples. The electrokinetic sample
injection was carried out at 10 kV per 10 s; UV absorbance detection was at
254 nm. Using standard samples, the creatinine migration mean time in 100
mmol/L acetate buffer, pH 4.4, was 3.3 +/- 0.2 min; the repeatability for a
bsolute migration mean time was 0.6% and peak height repeatability was 2.9%
. The correlation coefficient of the standard curve was r = 0.999 and the d
etection limit was 23.1 mu mol/L. Intra- and interassay coefficients of var
iation (CV) were 3.0 and 3.6%, respectively; recovery was 99 +/- 3% and lin
earity was r = 0.98. Normal urine samples were diluted 1:80 in run buffer.
The present CE urine creatinine assay showed a good correlation with HPLC a
nd with Jaffe methods (r = 0.98 and r = 0.97, respectively; p < 0.0001). Th
e uCr in the morning urine samples of 34 healthy males (M), 38 healthy fema
les (F), and 83 male athletes (A) was 10.4 +/- 6.1 mmol/L, 10.8 +/- 8.1 mmo
l/L and 13.2 +/- 6.5 mmol/L, respectively. The uCr difference (p < 0.02) be
tween M and A and a correlation (p < 0.05) with age in A were observed.