How long must the typical microhematocrit tube be centrifuged for packed cell volume determination?

• A. 1 minute
• B. 5 minutes
• C. 10 minutes
• D. 15 minutes

Answer: (B)

The idea is to use enough force and time to separate the red blood cells from the plasma so you can read a clean packed cell layer. For the microhematocrit method, spinning the capillary tube at a high g-forces (roughly 10,000–12,000 g) for about five minutes reliably yields a tightly packed red cell column with clear plasma above it. This creates a precise interface to read the packed cell volume (PCV). If you spin much less than five minutes, the cells don’t settle fully, giving a fuzzy interface and an inaccurate PCV. Spinning much longer isn’t typically necessary and can risk cell damage or other minor changes, but five minutes is the standard that gives reproducible, accurate results across most samples and labs.