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Reticulocyte count
Definition
A reticulocyte count measures the percentage of reticulocytes (slightly immature red blood cells) in the blood.
How the test is performed
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.
How to prepare for the test
No special preparation is necessary.
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.
Why the test is performed
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.
Normal Values
The normal range depends on the level of hemoglobin, and the range is higher if there is low hemoglobin due to bleeding or red cell destruction.
What abnormal results mean
A higher-than-normal percentage of reticulocytes may indicate:
- Bleeding
- Erythroblastosis fetalis
- Hemolytic anemia
- Kidney disease with increased erythropoietin production
A lower-than-normal percentage of reticulocytes may indicate:
- Bone marrow failure (for example, from drug toxicity, tumor, or infection)
- Cirrhosis of the liver
- Folate deficiency
- Iron deficiency
- Kidney disease with decreased erythropoietin production
- Radiation therapy
- Vitamin B-12 deficiency
Additional conditions under which the test may be performed:
- 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
What the risks are
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)
Special considerations
The reticulocyte count may be increased during pregnancy.
References
Zuckerman K. Approach to the anemias. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 162.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
