Why it's done

A hematocrit test is part of a complete blood count (CBC). Measuring the proportion of red blood cells in your blood can help your doctor make a diagnosis or monitor your response to a treatment.

A lower than normal hematocrit can indicate:

  • An insufficient supply of healthy red blood cells (anemia)
  • A large number of white blood cells due to long-term illness, infection or a white blood cell disorder such as leukemia or lymphoma
  • Vitamin or mineral deficiencies
  • Recent or long-term blood loss

A higher than normal hematocrit can indicate:

  • Dehydration
  • A disorder, such as polycythemia vera, that causes your body to produce too many red blood cells
  • Lung or heart disease