During the diuretic phase on days 2–3 of life, which factor causes a transient increase in FENA?

• A. Sepsis
• B. Oxygen therapy
• C. Diuretic phase
• D. Hypotension

Answer: (C)

During the diuretic phase, the kidneys are actively dumping sodium into the urine because of the diuretic effect and recovering tubular function. Diuretics block reabsorption of sodium in parts of the nephron, increasing sodium delivery to the distal nephron and its excretion. This natriuresis raises the fraction of filtered sodium that is excreted in the urine, so FENA goes up transiently on days 2–3 of life. Other factors like sepsis or hypotension can lower renal perfusion and often don’t produce this transient rise in FENA; oxygen therapy isn’t a primary driver of a transient FENA increase. The effect is temporary as tubular function and diuretic response evolve.