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A reticulocyte count is a blood test that measures how fast red blood cells, Opens dialog called reticulocytes, Opens dialog 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.

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, Opens dialog. Also, being at high altitudes may cause reticulocyte counts to rise, to help you adjust to the lower oxygen levels at high altitudes.

Why It Is Done

A reticulocyte count is done to:

• See whether anemia, Opens dialog is caused by fewer red blood cells being made or by a greater loss of red blood cells.
• Check how well bone marrow is working to make 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.

How To Prepare

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

How It Is Done

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 on the site and then put on a bandage.

How It Feels

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.

Risks

There is very little chance of a problem from having a 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.

Results

A reticulocyte count is a blood test that measures how fast red blood cells, Opens dialog called reticulocytes, Opens dialog 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).

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Results are ready in 1 day.

High values

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

Low values

• A low reticulocyte count may mean fewer red blood cells are being made by the bone marrow. This can be caused by aplastic anemia, Opens dialog 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.

What Affects the Test

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

• Taking certain medicines. Medicines that affect the results include ones used for Parkinson's disease, rheumatoid arthritis, fevers, malaria, and cancer chemotherapy.
• Getting radiation therapy.
• Taking sulfonamide antibiotics (such as Septra).
• Being pregnant.
• Having a recent blood transfusion.