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