Oliguria is defined as urine output below which amount per 24 hours?

• A. Output <400 mL/24h
• B. Output <1000 mL/24h
• C. Output <200 mL/24h
• D. Output >400 mL/24h

Answer: (A)

Oliguria means the kidneys are producing abnormally small amounts of urine. In adults, this is defined as urine output less than about 400 mL in 24 hours. This threshold is used because falling below 400 mL/day signals that the kidneys aren’t filtering effectively, which can point to dehydration, reduced renal perfusion, or early kidney injury and requires prompt assessment and management. Normal urine output is typically around 800–2000 mL per day (roughly 0.5 mL/kg/hr for many adults), so 400 mL/day is clearly low. Outputs much higher than 400 mL/day are not oliguria, while much lower outputs (like 200 mL/day) indicate more severe suppression of urine production.