What type of centrifuge head is used for microhematocrit tubes?

• A. Swinging bucket head
• B. Fixed angle head
• C. Horizontal rotor
• D. Ultracentrifuge

Answer: (B)

Microhematocrit tubes rely on a clear, compact separation of red cells from plasma. Using a fixed-angle head positions each capillary tube at a constant angle during spin, which promotes rapid and tight packing of the red cells at the bottom and a sharp interface with the plasma. This orientation gives a precise, easily readable hematocrit after centrifugation because the boundary between cellular and plasma portions lines up along the length of the tube.

A swinging-bucket head would let the tubes pivot to a vertical position during spinning, which can disturb the compact cell layer and make readings less reliable. A horizontal rotor serves other separation needs where tubes stay level, and ultracentrifuges are designed for much higher speeds not required for routine microhematocrit measurements.