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The hematocrit is a measure of the red blood cell mass, expressed as a percentage.

Blood is placed in a test tube and centrifuged to separate the heavier red blood cells from the lighter serum and plasma. The percentage of the blood volume occupied by the mass of red cells is the hematocrit.

Increased in the Presence of:

  • Hemoconcentration
  • COPD (chronic obstructive pulmonary disease)
  • CHF (congestive heart failure)
  • Smokers
  • Pre-eclampsia

Decreased in the Presence of:

  • Anemia
  • Leukemia
  • Hyperthryroidism
  • Chronic liver disease
  • Hemolysis:
    • Transfusion reaction
    • Drug/chemical reaction
    • Infection
    • Burns
    • Mechanical disruption (artificial heart valves)
  • Systemic Disease
    • Cancer
    • Lupus
    • Sardoidosis

Special Considerations

  • Smokers typically have elevated hematocrits in response to chronic, low-grade carbon monoxide poisoning and other mild respiratory ailments. Because of the carbon monoxide binding, they may still be functionally anemic, even though their hematocrit levels look good.
  • Adaptation to high altitudes includes moderate elevation of hematocrit.
  • During the initial phases of an acute hemorrhage, the hematocrit generally doesn't change very much. Later, as extracellular fluid is mobilized and IV fluids are incorporated, there is a dilutional effect that will lead to a reduced hematocrit. This fall in hematocrit may take several hours to develop.

Normal Values*

  Packed Cell Volume


Women 37%-47%
Pregnancy 33%-44%
Newborn 50%-62%

*These are general values taken from a variety of sources. The actual normal values may vary from lab to lab and from one type of testing protocol to another.


Source: Operational Medicine 2001,  Health Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington, D.C., 20372-5300