Low-output fistulas are typically defined as output under how many mL per day?

• A. 400 mL/day
• B. 800 mL/day
• C. <500 mL/day
• D. 1000 mL/day

Answer: (C)

The key idea is classifying fistula output to guide management of nutrition and fluids. Low-output fistulas are defined as less than 500 mL per day. This level of losses is small enough that patients can often continue oral or enteral nutrition with less risk of dehydration and electrolyte imbalance, and there’s a higher chance the fistula may close spontaneously. In contrast, higher outputs—such as 800 mL/day or 1000 mL/day—drive substantial fluid and electrolyte losses and usually require more aggressive management, including fluids, electrolytes, and often parenteral nutrition. So, the typical threshold used to call a fistula “low-output” is under 500 mL per day.