A hematocrit (he-MAT-uh-krit) test measures the proportion of red blood cells in your blood. Red blood cells carry oxygen throughout your body. Having too few or too many red blood cells can be a sign of certain diseases.

The hematocrit test, also known as a packed-cell volume (PCV) test, is a simple blood test.

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

The hematocrit is a simple blood test. You won't need to fast before the test or make other preparations.

The blood sample is generally drawn with a needle from a vein in your arm. You may feel some tenderness at the site, but you'll be able to resume normal activities afterward.

Results from your hematocrit test are reported as the percentage of blood cells that are red blood cells. Normal ranges vary substantially with race, age and sex. The definition of normal red-blood cell percentage also varies from one medical practice to another.

Generally, a normal range is considered to be:

• For men, 38.3 to 48.6 percent
• For women, 35.5 to 44.9 percent

For children ages 17 and younger, the normal range varies by age and sex.

Your hematocrit test provides just one piece of information about your health. Talk to your doctor about what your hematocrit test result means in light of the symptoms you're experiencing and the results of other diagnostic tests.

Accuracy of test results

A number of factors can affect the outcome of a hematocrit test and yield inaccurate or misleading results, including:

• Living at a high altitude
• Pregnancy
• Significant recent blood loss
• Recent blood transfusion
• Severe dehydration

Your doctor will take into account possible complicating factors when interpreting the results of your hematocrit test. Your doctor may want to repeat the hematocrit test and do other blood tests if results provide conflicting or unexpected information.