A rapid urine creatinine assay by capillary zone electrophoresis

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.