Which venous lumen size is specifically recommended for a fistula, not a graft?

• A. Greater than or equal to 2.0 mm
• B. Greater than or equal to 2.4 mm
• C. Greater than or equal to 2.5 mm
• D. Greater than or equal to 3.0 mm

Answer: (C)

A fistula relies on the native vein to remodel and dilate under higher flow, so having a vein large enough to handle those changes is crucial for successful maturation. Preoperative ultrasound mapping guides whether a vein can mature into a durable access. The widely cited minimum lumen diameter for a native AV fistula is about two and a half millimeters. Veins at or above this size have a better chance to mature and stay patent, while smaller veins tend to fail to mature or thrombose, making a graft or a different site more appropriate. Grafts can be placed with smaller veins because they don’t depend on native venous remodeling, which is why the two-and-a-half millimeter threshold is described specifically for fistulas rather than grafts.