Hematocrit is the proportion of your total blood volume that is composed of red blood cells. A hematocrit (HCT) test indicates whether you have too few or too many red blood cells — conditions that can occur as the result of certain diseases. Red blood cells, or erythrocytes, transport oxygen throughout your body.
A hematocrit test is part of a complete blood count (CBC). The proportion of red blood cells compared with all blood cells may help your doctor make a diagnosis or monitor your response to a treatment.
What a lower than normal hematocrit may indicate
- An insufficient supply of healthy red blood cells (anemia)
- A large number of white blood cells — usually a very small portion of your blood — due to long-term illness, infection, leukemia, lymphoma or other disorders of white blood cells
- Vitamin or mineral deficiencies: Nutrition deficiencies of iron, copper, folic acid, vitamin B6, or vitamin B12
- Recent or long-term blood loss
- Deficiency of a hormone called erytropoietin (caused by kidney disease)
What a high hematocrit means
- Dehydration (such as from severe diarrhea)
- A disorder, such as polycythemia vera, that causes your body to produce too many red blood cells
- Lung or heart disease. If the body senses low oxygen levels, it will make more red blood cells in an effort to increase the amount of oxygen in the blood.
- Cigarette smoking
- Kidney tumor
How is a low or high hematocrit treated?
The treatment of high or low hematocrit depends on the underlying cause, the hematocrit level, and the overall health status of the individual. Some patients with very low hematocrits may require intravenous iron or complete blood count. Some patients with very high hematocrits due to diseases, such as polycythemia rubra vera, may require blood letting.
The doctor will decide when medication or procedures are necessary for each particular individual. In general, abnormal hematocrit values are monitored by doctors with routine blood testing.