Urinary dilution capability in term newborns compared with older children or adults is:

• A. Similar
• B. Diminished
• C. Exaggerated
• D. Not comparable

Answer: (A)

Term newborns have a preserved ability to dilute urine, so their capacity to excrete free water under flowing conditions is similar to that of older children and adults. This contrasts with their still immature concentrating ability, which is limited in the neonatal period due to immature medullary gradient and tubular function. In other words, when water is available, a term newborn can produce relatively dilute urine much like older individuals, even though their urine concentration under dehydration can lag behind adults.