Urinary sodium to creatinine ratio in healthy infants

Rationale. Sodium is essential for adequate growth; the daily requirement in infants is 2 to 3 mmol/kg/d. Objectives. The study aimed to establish a reference range for the ratio of urinary sodium (UNa) to creatinine (UCr) in healthy infants in a suburban setting in the United States. Methods. UNa and UCr were measured in healthy infants and UNa:UCr was calculated. Daily sodium intake was estimated by parental report. Results. Mean estimated sodium intake in the 71 infants was 1.34 mEq/kg/d (95% confidence interval = 1.23-1.44). The mean UNa:UCr was 11.73 (95% confidence interval = 10.24-13.23) and did not differ significantly in age-groups. There was no direct correlation between sodium intake and UNa:UCr in healthy infants. Conclusions. The UNa:UCr was 11.73 in this population of healthy infants. This likely reflects the appropriate physiologic response to sodium intake in the study population, which was at the lower end of the usual estimated needs for infants.