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.

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

No special preparation is necessary for adults.

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.

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

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

Additional conditions under which an RBC count 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

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

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

• Cigarette smoking
• Congenital heart disease
• Cor pulmonale
• Dehydration (such as from severe diarrhea)
• Kidney tumor (renal cell carcinoma)
• Low blood oxygen levels (hypoxia)
• Pulmonary fibrosis
• Polycythemia vera

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

Drugs that can increase the RBC count include:

• Gentamicin
• Methyldopa

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

• Anemia
• Bone marrow failure (for example, from radiation, toxins, or tumor)
• Erythropoietin deficiency (secondary to kidney disease)
• Hemolysis (RBC destruction) due to transfusion, blood vessel injury, or other cause
• Hemorrhage (bleeding)
• Leukemia
• Malnutrition
• Multiple myeloma
• Nutritional deficiencies of:
  • Iron
  • Copper
  • Folate
  • Vitamin B-12
  • Vitamin B-6
• Overhydration
• Pregnancy

Drugs that can decrease the RBC count include:

• Chloramphenicol
• Hydantoins
• Quinidine

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood 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 light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Zuckerman K. Approach to the anemias. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 162.