Measurement of purines in urine by capillary electrophoresis for estimating the degree of hypoxia in infants.

We describe a simple, rapid and reproducible method for measuring hypoxanthine, xanthine and uric acid in urine samples of infants by capillary electrophoresis with an uncoated fused silica capillary and ultraviolet detection. Conditions were 40 mmol/l borate buffer pH 9.4 with sodium dodecyl sulphate (0.1 mol) 3 s hydrodynamic load and the voltage 20 kV. The calibration curves for hypoxanthine and xanthine were linear to 150 micromol/l and for uric acid to 300 micromol/l. The limits of detection for hypoxanthine, xanthine and uric acid were 0.5, 2.0 and 20 micromol/l, respectively. Analytical recovery of the three purines ranged from 93 to 105%. Overall CVs were < 5.2%. Using this method, we measured purine concentrations in the urine samples of 103 infants, divided into three groups, according to different degrees of hypoxia. There was a significant difference among the three groups only in hypoxanthine concentrations. In 35 urine samples from the control group, 43 urine samples from infants with a history of an apparent life threatening episode and in 25 urine samples from infants with infantile apnoea, the mean concentrations of hypoxanthine (mean +/- SD) were 13.1 +/- 4.0, 25.1 +/- 8.1 and 58.2 +/- 17.4 micromol/mmol creatinine, respectively. The diagnostic accuracy of the purine measurement was evaluated by receiver-operating characteristic curve analysis.