Health Encyclopedia

RBC count

Definition

An RBC count is a blood test that tells how many red blood cells (RBCs) you have.

RBCs contain hemoglobin, which carries oxygen. How much oxygen your body tissues get depends on how many RBCs you have and how well they work.

Alternative Names

Erythrocyte count; Red blood cell count

How the test is performed

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore blood flow. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child:

The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to prepare for the test

No special preparation is necessary for adults.

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Veins and arteries vary in size from one patient 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.

Why the test is performed

This test can help diagnose anemia and other conditions affecting red blood cells.

The RBC count is almost always part of the CBC (complete blood count) test.

Normal Values

Normal results vary, but in general the range is as follows:

Male: 4.7 to 6.1 million cells per microliter (cells/mcL)
Female: 4.2 to 5.4 million cells/mcL

What abnormal results mean

Damaged RBCs do not live as long as normal. Injury inside the blood vessels, such as that caused by artificial heart valves or peripheral blood vessel disease, can damage RBCs.

Higher-than-normal numbers of RBCs may be due to:

Congenital heart disease
Cor pulmonale
Dehydration (such as from severe diarrhea)
Pulmonary fibrosis
Polycythemia vera

Lower-than-normal numbers of RBCs may be due to:

Anemia (various types)
Bone marrow failure (for example, from radiation, toxin, or tumor)
Erythropoietin deficiency (secondary to kidney disease)
Hemolysis (RBC destruction) from transfusion reaction
Hemorrhage (bleeding)
Leukemia
Malnutrition
Multiple myeloma
Nutritional deficiencies of:
- Iron
- Copper
- Folate
- Vitamin B-12
- Vitamin B-6
Overhydration

Additional conditions under which the test may be performed:

Alport syndrome
Drug-induced immune hemolytic anemia
Hemolytic anemia due to G6PD deficiency
Hereditary anemias, such as thalassemia
Idiopathic autoimmune hemolytic anemia
Immune hemolytic anemia
Macroglobulinemia of Waldenstrom
Paroxysmal nocturnal hemoglobinuria (PNH)
Primary myelofibrosis
Renal cell carcinoma

What the risks are

Excessive bleeding
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Multiple punctures to locate veins

Special considerations

Pregnancy can cause a decrease in RBCs.

Your RBC count will increase for several weeks when you move to a higher altitude. Dehydration also increases the RBC count.

Drugs can increase the RBC count include:

Gentamicin
Methyldopa

Drugs that can decrease the RBC count include:

Chloramphenicol
Hydantoins
Quinidine

References

McPherson RA and Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: WB Saunders; 2007:461-2.

Hoffman R, Benz Jr. EJ, Shattil SJ, et al., eds. Hematology: Basic Principles and Practice. 4th ed. Philadelphia, Pa: Churchill Livingston; 2005:2733.

Review Date:3/8/2007
Reviewed By:Mark Levin, MD, Hematologist and Oncologist, Newark, NJ. Review provided by VeriMed Healthcare Network.

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