Hematocrit

Overview

Hematocrit measures the volume percentage of packed red blood cells in whole blood after centrifugation, reflecting erythroid mass and oxygen-carrying capacity. It correlates directly with hemoglobin concentration and varies with hydration status, altitude, and erythropoietic activity. Elevated levels indicate polycythemia (dehydration, hypoxia, myeloproliferative disorders), while low levels signal anemia from blood loss, hemolysis, or bone marrow failure. Hematocrit is clinically essential for anemia/polycythemia diagnosis, transfusion guidance, and monitoring hydration and chronic disease states.

Clinical Use Cases

  • Diagnosing and classifying anemia severity.
  • Evaluating polycythemia vera vs relative polycythemia.
  • Monitoring blood loss, transfusion response, and chemotherapy effects.
  • Assessing hydration status and phlebotomy needs.

Specimen Types

  • Whole blood (EDTA K2/K3).
  • Capillary blood (point-of-care).

Measurement Methods

  • Automated hematology analyzer (impedance, flow cytometry).
  • Microhematocrit centrifugation (capillary tube).
  • Calculated from RBC count and MCV (rHct).

Test Preparation and Influencing Factors

  • No fasting required.
  • Dehydration, smoking, high altitude elevate levels.
  • Recent blood loss, pregnancy, or overhydration decrease levels.
  • Posture (standing vs supine) and tourniquet time affect results.

Synonyms

  • Hct.
  • Packed cell volume (PCV).
  • Erythrocyte volume fraction.

Further Reading

  • Hematocrit Test; MedlinePlus;