Hyponatremia in neonates with renal failure is typically related to which factor?

• A. Dehydration
• B. Increased secretion of antidiuretic hormone (ADH)
• C. Polyuria
• D. Renal immaturity

Answer: (B)

Hyponatremia in neonates with renal failure is driven by increased ADH secretion leading to water retention and dilution of serum sodium. Antidiuretic hormone acts on the collecting ducts to insert aquaporin-2 channels, promoting reabsorption of free water. When ADH levels are elevated, the kidneys conserve more water, which lowers plasma sodium concentration. In renal failure, the ability to excrete this excess water is impaired, so the dilutional effect is amplified. Neonates can have nonosmotic ADH release in response to stress or illness, further contributing to hyponatremia.

Dehydration would more commonly cause hypernatremia or normal-to-low-normal sodium depending on fluid losses; polyuria tends to lead to free-water loss and can cause hypernatremia if water intake doesn’t keep up; renal immaturity affects concentrating ability but doesn’t specifically explain dilutional hyponatremia driven by ADH in the setting of renal failure.