Hematocrit

A blood sample is needed.

No special preparation is necessary for this test.

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.

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 anemia or a condition that increases your risk for anemia. These include:

• 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 vary, but in general they are:

• Male: 37% to 48%
• Female: 34% to 43%

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 labs. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.

A low hematocrit (anemia) may be due to:

• Bleeding
• 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
• Malnutrition
• Pregnancy
• Deficiency of copper, iron, folate, vitamin B12, or vitamin B6
• Too much water in the body

A 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 at a higher altitude.

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)

HCT

Lin JC, Benz EJ Jr. Approach to anemia in the adult and child. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 35.

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.

Updated by: Jacob Berman, MD, MPH, Associate Professor of Medicine, Division of General Internal Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.