Hematokrit

Hematocrit, often abbreviated Hct, is the proportion of whole blood occupied by red blood cells. It is expressed as a percentage of the total blood volume. For example, a hematocrit of 42% means that 42% of the blood’s volume consists of red blood cells.

Measurement is typically done by centrifuging a sample of anticoagulated blood in a capillary tube to separate plasma, a buffy coat, and packed red cells; the height of the packed red cell layer divided by the total height yields the hematocrit. Automated hematology analyzers estimate hematocrit from measurements of red blood cell count and mean corpuscular volume, or directly by impedance or optical methods on modern platforms.

Normal ranges vary by age, sex, altitude, and physiological state. In healthy adults, typical reference ranges are roughly 40–54% for men and 36–46% for women. Newborns and children have different norms, and values can be affected by hydration status and pregnancy. Clinicians interpret hematocrit alongside other tests such as hemoglobin concentration.

Clinical use and interpretation: low hematocrit suggests anemia due to decreased RBC production, increased destruction, or blood loss; high hematocrit can indicate polycythemia or reduced plasma volume due to dehydration or diuretic use. Hematocrit is often considered with reticulocyte count and red blood cell indices to determine the cause of abnormal values.

Limitations include potential measurement variability between methods and factors such as severe dehydration, polycythemia vera, or abnormal red blood cell morphology that can affect accuracy. Values should be interpreted in the broader clinical context.