Reticulocyte Count

A reticulocyte count is a blood test that measures how fast red blood cells called reticulocytes are made by the bone marrow and released into the blood. Reticulocytes are in the blood for about 2 days before developing into mature red blood cells. Normally, about 1% to 2% of the red blood cells in the blood are reticulocytes.

The reticulocyte count rises when there is a lot of blood loss or in certain diseases in which red blood cells are destroyed prematurely, such as hemolytic anemia. Also, being at high altitudes may cause reticulocyte counts to rise, to help you adjust to the lower oxygen levels at high altitudes.

A reticulocyte count is done to:

• See whether anemia is caused by fewer red blood cells being made or by a greater loss of red blood cells.
• Check to see if treatment for anemia is working. For example, a higher reticulocyte count means that iron replacement treatment or other treatment to reverse the anemia is working.

You do not need to do anything before you have this test.

The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure to the site and then a bandage.

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

There is very little chance of a problem from having blood sample taken from a vein.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

A reticulocyte count is a blood test that measures how fast red blood cells called reticulocytes are made by the bone marrow and released into the blood.

Normal

The reticulocyte count is given as the percentage of red blood cells that are reticulocytes (the number of reticulocytes divided by the total number of red blood cells, multiplied by 100).

Normal values may vary from lab to lab. Results are ready in 1 day.

Newborns have a normal reticulocyte count of 2.5% to 6.5%. This value drops within 2 weeks to 0.5% to 2.0%.

High values

• A high reticulocyte count may mean more red blood cells are made by the bone marrow. This can occur after a lot of bleeding, a move to a high altitude, or certain types of anemia. These conditions cause red blood cells to break down (hemolysis).
• The reticulocyte count rises after the treatment for pernicious anemia, iron deficiency anemia, or folic acid deficiency anemia starts working.

Low values

• A low reticulocyte count may mean fewer red blood cells are made by the bone marrow. This can be caused by aplastic anemia or other types of anemia, such as iron deficiency anemia.
• A low reticulocyte count can also be caused by exposure to radiation, a long-term (chronic) infection, or by certain medicines that damage the bone marrow.

Reasons you may not be able to have the test or why the results may not be helpful include:

• Taking medicines, such as levodopa, corticotropin, azathioprine (Imuran), chloramphenicol (Chloromycetin), dactinomycin (Cosmegen), medicines to reduce a fever, medicines to treat malaria, and methotrexate and other cancer chemotherapy medicines.
• Getting radiation therapy.
• Taking sulfonamide antibiotics (such as Bactrim or Septra).
• Being pregnant.
• Having a recent blood transfusion.

• In anemia, the reticulocyte count will be abnormal because the levels of red blood cells and hemoglobin are low. Also, reticulocytes make up a higher percentage of the blood count in anemia, which makes the reticulocyte count falsely high. For this reason, a doctor will check the reticulocyte count along with the reticulocyte index (RI) when checking for anemia. The RI is a measurement for reticulocytes when anemia is present.
• A reticulocyte count may help a doctor decide other tests that need to be done to diagnose a specific type of anemia or other disease. A low reticulocyte count may mean a need for a bone marrow biopsy. This can tell if there is a problem with how new reticulocytes are made by the bone marrow. For more information, see the medical test Bone Marrow Aspiration and Biopsy.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.