Urine Output Thresholds

Clinical Definitions

Oliguria is defined as <0.5 mL/kg/hour sustained over at least 6 hours, which translates to approximately <400 mL per day in a 70 kg adult, according to the Praxis Medical Insights guidelines 1
Anuria is defined as 24-hour urine volume less than 100 mL, as stated by the American Journal of Kidney Diseases 2
The American College of Physicians guidelines imply that these thresholds apply to total daily output, not individual void volumes, similar to the Praxis Medical Insights guidelines 1

Normal nighttime voiding produces normal or large volume voids when nocturnal polyuria is present (>33% of 24-hour output occurring at night), as noted by the Praxis Medical Insights guidelines 3, 4
Small volume voids throughout day and night suggest reduced bladder capacity rather than polyuria, according to the Praxis Medical Insights guidelines 4

The Praxis Medical Insights guidelines recommend not confusing single void volume with hourly urine output rates, as these measure different physiologic parameters, with single void volume reflecting bladder capacity and voiding habits, and hourly output rates assessing kidney function and perfusion 1