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.

Why It Is Done

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 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 to the site and then 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 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.