The identification of hyperoxaluria in very low-birthweight infants--which urine sampling method?

The present study was performed to determine the best method of urine collection for measurement of oxalate excretion in very low-birthweight (VLBW) infants and to verify the utility of the oxalate/creatinine ratio in VLBW infants. This has not been investigated in this group with developing renal function. In a prospective study of 30 VLBW infants, we compared oxalate excretion in urine collected over 24 h and in a spot urine sample. The urinary oxalate concentration was measured by the oxalate oxidase method. The correlation coefficient between the amount of oxalate per kilogram body weight excreted daily and the oxalate/creatinine ratio in spot urine sample was 0.80 (P < 0.0001) and with the oxalate/creatinine ratio in a 24-h urine collection 0.82 (P < 0.0001). The two highest levels of oxalate excretion (> 100 mumol/kg per day) were detected with both oxalate/creatinine ratios (> 1 mmol/ mmol). No circadian rhythm of oxalate excretion was found. The measurement of the oxalate/creatinine ratio in spot urine samples is suitable for screening VLBW infants for hyperoxaluria.