Anuria is defined as urine output of less than how many milliliters per 24 hours?

• A. Output <400 mL/24h
• B. Output <50 mL/24h
• C. Output <100 mL/24h
• D. Output <200 mL/24h

Answer: (C)

The key idea is how urine production thresholds are used to classify kidney function. Anuria means the kidneys are producing very little urine over a day, specifically fewer than 100 mL in 24 hours. This level is distinguishable from oliguria, which is a reduced amount of urine but not this low (often less than 400 mL per day). The 100 mL mark reflects a minimal output below which the body's waste products can accumulate and fluid balance can become severely disrupted, signaling a potentially urgent problem that needs prompt evaluation.

So, urine output under 100 mL in 24 hours defines anuria. Output around 400 mL per day points to oliguria, and outputs like 50 mL or 200 mL are not the standard definition for anuria.