Where is the hematocrit value typically measured in a microhematocrit tube?

The hematocrit value is measured at the interface of plasma and red blood cells in a microhematocrit tube. This is because the hematocrit is defined as the percentage of blood volume that is occupied by red blood cells. When a blood sample is centrifuged in a microhematocrit tube, the heavier red blood cells settle at the bottom, forming a distinct layer. Above this layer lies the plasma, which is lighter.

The measurement at the interface allows for an accurate assessment of the proportion of red blood cells compared to the total volume of blood in the tube, which is crucial for diagnosing conditions such as anemia or polycythemia. This standard practice ensures consistency and reliability in hematocrit measurements, which are vital for clinical evaluations of a patient’s health.