Compared with an adult, a full-term neonate has a markedly reduced ability to concentrate urine. The approximate maximum urine osmolality achievable by a normal term neonate is closest to:

• A 300 mOsm/kg
• B 450 mOsm/kg
• C 700 mOsm/kg ✓
• D 1200 mOsm/kg

Explanation

The term neonate can concentrate urine to roughly 600 to 750 mOsm/kg, about half the adult maximum of 1200 mOsm/kg, because of a shorter loop of Henle, low urea gradient in the inner medulla and relative ADH responsiveness limitations. Adult capacity is reached over the first months to a year. A ceiling near 300 mOsm/kg would indicate frank renal failure, and 1200 mOsm/kg is the mature adult value, not the neonatal one.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.