Hematocrit is a blood test that measures how much of a person's blood is made up of red blood cells. This measurement depends on the number of and size of the red blood cells.
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
No special preparation is necessary for this test.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
Why the Test is Performed
The hematocrit is almost always done as part of a complete blood count (CBC).
Your health care provider may recommend this test if you have signs of or are at risk for anemia. These ionclude having:
- Grumpiness or tiredness
- Problems concentrating
- Poor nutrition
- Heavy menstrual periods
- Blood in your stools, or vomit (if you throw up)
- Treatment for cancer
- Leukemia or other problems in the bone marrow
- Chronic medical problems, such as kidney disease or certain types of arthritis
Normal results vary, but in general they are:
- Male: 40.7% to 50.3%
- Female: 36.1% to 44.3%
For babies, normal results are:
- Newborn: 45% to 61%
- Infant: 32% to 42%
The examples above are common measurements for results of these tests. Normal value ranges vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
What Abnormal Results Mean
Low hematocrit may be due to:
- Destruction of red blood cells
- Too little iron, folate, vitamin B12, and vitamin B6 in the diet
- Too much water in the body
High hematocrit may be due to:
- Congenital heart disease
- Failure of the right side of the heart
- Too little water in the body (dehydration)
- Low levels of oxygen in the blood
- Scarring or thickening of the lungs
- Bone marrow disease that causes abnormal increase in red blood cells
Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood buildup under the skin)
- Infection (a slight risk any time the skin is broken)
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Kumar V, Abbas AK, Aster JC. Red blood cell and bleeding disorders. In: Kumar V, Abbas AK, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 14.
Maheshwari A, Carlo WA. Blood disorders. In: Kliegman RM, Stanton BF, St Geme JW, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2015:chap 103.