What is a safe bleed volume for a 20-gram mouse?

• A. 0.01 ml
• B. 0.1-0.2 ml
• C. 0.25 ml
• D. 0.5 ml

Answer: (B)

A small fraction of the mouse’s blood is safely removable at one time. A typical mouse has blood volume around 7–8% of its body weight, so a 20 g mouse holds roughly 1.4–1.6 mL of blood. To avoid causing hypovolemia, a single draw is kept to about 10% of that blood volume, which is about 0.14–0.16 mL. In practice, this is taken as a safe range of roughly 0.1–0.2 mL for a 20 g mouse.

Choosing a much smaller volume would often yield inadequate sample for tests, while larger volumes like 0.25 mL or 0.5 mL risk significant blood loss.