Hematocrit

Overview

What is a hematocrit test?

A hematocrit is a simple blood test done to measure the red blood cells in a person’s blood. Red blood cells (erythrocytes) are important because they carry oxygen through your body. A low or high red blood cell count can indicate a medical condition or disease.

The hematocrit test determines the number of red blood cells.

Why is a hematocrit test needed?

A hematocrit test is needed to check for the proportion of red blood cells. A low red blood cell count, or low hematocrit, indicates anemia. Suspected anemia is the most common reason for hematocrit testing.

A hematocrit is sometimes called a HCT. The hematocrit is calculated from the number of red blood cells in a sample of blood.

What is anemia?

Anemia is a condition in which the body does not have enough red blood cells to carry oxygen through the body. It can have many causes, including iron and vitamin deficiency.

Symptoms of anemia include:

  • Tiredness
  • Headaches
  • Trouble concentrating
  • Cold hands and feet
  • Fatigue
  • Shortness of breath
  • Chest pain
  • Dizziness or lightheadedness

Test Details

How do I prepare for a hematocrit test?

No preparations are needed for a hematocrit test. Your physician will perform the test in his or her office or send you to a lab for testing.

A hematocrit is usually done as part of a complete blood count (CBC).

What can I expect during a hematocrit test?

The lab technician will begin the test by cleaning the area for the blood draw. This will usually be on the inside of your arm.

When the needle is inserted to draw blood, you might feel a prick or moderate pain. You may bruise afterwards. The technician will cover the draw site with gauze and a small bandage.

Are there risks to a hematocrit test?

A hematocrit is a very safe, common test. All tests carry a slight risk, however. These include:

  • Feeling faint
  • Excessive bleeding
  • A hematoma
  • Infection

Results and Follow-Up

What are normal hematocrit test results?

The range for normal tests varies due to age and gender, but the general guidelines are:

  • Male: 41% to 50%
  • Female: 36% to 44%

For babies, normal results are:

  • Newborn: 45% to 61%
  • Infant: 32% to 42%

Your doctor will determine what is normal for you or your child.

What if I get a hematocrit result outside of the normal range?

Hematocrit results outside of the normal range, whether low or high, can indicate a serious medical condition. Your healthcare provider can interpret your individual results and come up with the best treatment plan for your underlying condition.

Low hematocrit results can indicate:

  • Blood loss
  • Leukemia or other bone marrow problems
  • Iron and vitamin deficiency, including folate, vitamin B12, and vitamin B6
  • Too much water in the body
  • Kidney disease
  • Thyroid abnormality
  • Immune destruction of red blood cells

High hematocrit may be due to:

  • Heart disease
  • Dehydration
  • Scarring or thickening of the lungs
  • Bone marrow disease
  • Obstructive sleep apnea
  • Smoking
  • Carbon monoxide poisoning
  • Testosterone use

Last reviewed by a Cleveland Clinic medical professional on 01/12/2018.

References

  • Billett HH. Hemoglobin and Hematocrit. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Accessed 2/13/2018.Chapter 151. (https://www.ncbi.nlm.nih.gov/books/NBK259/)

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