A reticulocyte count measures the percentage of reticulocytes (slightly immature red blood cells) in blood.

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.

The blood sample is sent to a laboratory. A special stain is used to identify the reticulocytes.

No special preparation is necessary.

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 test is done to determine if red blood cells are being created in the bone marrow at an appropriate rate. The number of reticulocytes in the blood is a sign of how quickly they are being produced and released by the bone marrow.

The normal range depends on the level of hemoglobin, and the range is higher if there has been bleeding or red cell destruction.

A higher-than-normal percentage of reticulocytes may indicate:

• Bleeding
• Erythroblastosis fetalis
• Hemolytic anemia
• Kidney disease with increased erythropoietin production

• Bone marrow failure (for example, from toxicity, tumor, or infection)
• Cirrhosis of the liver
• Folate deficiency
• Iron deficiency
• Kidney disease with decreased erythropoietin production
• Radiation therapy
• Vitamin B-12 deficiency

• Anemia of chronic disease
• Congenital spherocytic anemia
• Drug-induced immune hemolytic anemia
• Hemolytic anemia due to G6PD deficiency
• Idiopathic aplastic anemia
• Idiopathic autoimmune hemolytic anemia
• Immune hemolytic anemia
• Pernicious anemia
• Secondary aplastic anemia

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)

The reticulocyte count may be increased during pregnancy.

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