Hematocrit tubes are used to calculate which measurement in a blood sample?

• A. PCV (Packed Cell Volume)
• B. WBC count
• C. Platelet count
• D. Hemoglobin concentration

Answer: (A)

Hematocrit tubes are used to determine the proportion of blood that is made up by red blood cells, which is the packed cell volume (PCV). By spinning the tube, the blood separates into plasma, a thin buffy coat of white cells and platelets, and a tightly packed layer of red blood cells. Measuring the height of the red cell layer relative to the total blood column and expressing it as a percentage gives the PCV or hematocrit value. This is different from WBC or platelet counts, which require counting the cells in the buffy coat or with specialized counters, and from hemoglobin concentration, which is measured with a different method that analyzes the blood’s oxygen-carrying protein after lysing cells.