Pyrimidinea ppea rst o be especiallyi mportanti n the neonatal period, but the reference ranges for urinary pyrimidines have not been reported. We measured urinary pyrimidines in 23 healthy newborns on 6 successive days after birth (from day 0 to day 6) and at 1month of age. We also analyzed newborns with urea cycle disorders including ornithine transcarbamylase (OTC) deficiency. We measured urine samples using high-performancel iquid chromatographyw ith column switching. The reference ranges for urinary orotic acid, uracil and pseudouridine were determined. Orotic acid was greatly increased in OTC deficiency cases, but not in carbamoyl phosphate synthetas I deficiency. We speculate that urinary pyrimidine comcentrations is a useful index for diagnosis in the neonatal period.
