Urinary nitrite/nitrate excretion in infancy: Comparison between term and preterm infants

We measured urinary nitrite/nitrate (NOx^-) excretion, an index of endogenous nitric oxide formation, in term and preterm infants aged 1 week and 1, 4, 7 months, In normal term infants, urinary NOx^- excretion increased from 1 week to 1 month and then decreased until 4 months where it stabilized thereafter. Urinary NOx^- excretion in preterm infants was significantly higher compared with term infants at 1 week of age. This finding suggests that the nitric oxide pathway in preterm infants may be activated compared with term infants in early life. With the reference values obtained in this study, this urinary marker can now be used for identifying infants with abnormal nitric oxide production.