Which of the following is the correct threshold used to define high-output fistulas for PN indication?

• A. Greater than 100 mL/day
• B. Greater than 250 mL/day
• C. Greater than 750 mL/day
• D. Greater than 500 mL/day

Answer: (D)

High-output fistulas cause large volumes of fluid, electrolyte, and protein losses, which quickly push a patient toward malnutrition if nutrition intake isn’t able to keep up. When fistula output exceeds about 500 mL per day, oral or standard enteral nutrition is usually insufficient to meet energy and protein needs, so parenteral nutrition becomes indicated to maintain nitrogen balance and support healing.

Lower outputs (around 100–250 mL/day) are typically managed with enteral strategies and fistula care, since losses aren’t usually enough to demand PN. A threshold like 750 mL/day is indeed a high-output situation, but the commonly used tipping point for PN indication is around 500 mL/day because it best identifies those at risk of malnutrition who would benefit from parenteral support.