Hematocrit
HCTHematocrit is a blood test that measures how much of a person's blood is made up of red blood cells as opposed to plasma. This measurement depends on the number of and size of the red blood cells.
The number of and size of the red blood...
An RBC count is a blood test that measures how many red blood cells (RBCs) you have. RBCs contain hemoglobin, a protein which carries oxygen. How mu...
How the Test is Performed
A blood sample is needed.
Blood sample
Venipuncture is the collection of blood from a vein. It is most often done for laboratory testing.
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).
CBC
A complete blood count (CBC) test measures the following:The number of white blood cells (WBC count)The number of red blood cells (RBC count)The numb...
Your health care provider may recommend this test if you have signs of or are at risk for anemia. These include having:
- Before and after major surgery
- Blood in your stools, or vomit (if you throw up)
- Chronic medical problems, such as kidney disease or certain types of arthritis
- During pregnancy
- Fatigue, poor health, or unexplained weight loss
- Headaches
- Heavy menstrual periods
- Leukemia or other problems in the bone marrow
- Monitoring during treatment for cancer
- Monitoring medicines that may cause anemia or low blood counts
- Monitoring of anemia and its cause
- Poor nutrition
- Problems concentrating
Normal Results
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:
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Anemia
Anemia
Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. Different type...
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- Bone marrow being unable to produce new red blood cells. This may be due to leukemia, other cancers, medicine toxicity, radiation therapy, infection, or bone marrow disorders
- Chronic illness
- Chronic kidney disease
- Destruction of red blood cells (hemolysis)
- Leukemia
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Malnutrition
Malnutrition
Malnutrition is the condition that occurs when your body does not get enough nutrients.
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- Too little iron, folate, vitamin B12, and vitamin B6 in the diet
- Too much water in the body
High hematocrit may be due to:
- Bone marrow disease that causes abnormal increase in RBCs (polycythemia vera)
- Cigarette smoking
- Dehydration (for example, from severe diarrhea)
- Failure of the right side of the heart (cor pulmonale)
- Kidney tumor (renal cell carcinoma)
- Low blood oxygen level (hypoxia)
- Problem with heart's structure and function that is present at birth (congenital heart disease)
- Scarring or thickening of the lungs (pulmonary fibrosis)
Your hematocrit will increase for several weeks when you are in a higher altitude.
Risks
There is little risk involved with having your blood taken. 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
- Multiple punctures to locate veins
- Hematoma (blood buildup under the skin)
- Infection (a slight risk any time the skin is broken)
References
Means RT Jr. Approach to the anemias. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 144.
Thom CS, Lambert MP. Blood disorders. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 138.
Vajpayee N, Graham SS, Bem S. Basic examination of blood and bone marrow. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 31.
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Formed elements of blood - illustration
Blood transports oxygen and nutrients to body tissues and returns waste and carbon dioxide. Blood distributes nearly everything that is carried from one area in the body to another place within the body. For example, blood transports hormones from endocrine organs to their target organs and tissues. Blood helps maintain body temperature and normal pH levels in body tissues. The protective functions of blood include clot formation and the prevention of infection.
Formed elements of blood
illustration
-
Formed elements of blood - illustration
Blood transports oxygen and nutrients to body tissues and returns waste and carbon dioxide. Blood distributes nearly everything that is carried from one area in the body to another place within the body. For example, blood transports hormones from endocrine organs to their target organs and tissues. Blood helps maintain body temperature and normal pH levels in body tissues. The protective functions of blood include clot formation and the prevention of infection.
Formed elements of blood
illustration
Review Date: 3/11/2024
Reviewed By: Frank D. Brodkey, MD, FCCM, Associate Professor, Section of Pulmonary and Critical Care Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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