A reticulocyte count test measures the number of new red blood cells in your body. It’s sometimes called a reticulocyte index – or “retic count” for short. Doctors use it to help figure out whether you have certain types of illnesses that affect your blood, such as hemolytic anemia, a condition where red blood cells are destroyed faster than they can be made.
Your blood includes many kinds of cells, but red blood cells are the most common. They carry oxygen from your lungs to the rest of your body. The iron-rich protein called hemoglobin that carries oxygen in the red blood cells is what makes our blood red.
Because red blood cells only live about 4 months, your body constantly makes new ones, which are known as reticulocytes. They are bigger than mature red blood cells and are made by bone marrow, a spongy tissue inside many of your bones.
When doctors want to know whether your bone marrow is making the right amount of red blood cells, they take a sample of blood and calculate the number of reticulocytes in it. If you’re like most people, reticulocytes make up about 0.5% to 1.5% of your red blood cells.
What Happens in a Reticulocyte Count Test?
When you get this test, a lab tech will take a sample of blood from one of your veins.
In earlier years, doctors would put a drop of blood on a microscope slide and count the number of reticulocytes themselves. Today, machines calculate the results of nearly all reticulocyte count tests.
Why You Might Get One
A reticulocyte count test is often done when someone is believed to have an illness called anemia, which happens when your body doesn’t make enough red blood cells. That can leave you feeling weak and tired, short of breath, or having headaches and chest pain.
There are many different kinds of anemia. If your complete blood count suggests you have anemia, a reticulocyte count is one of several tests that can help tell your doctor which type:
- Aplastic anemia: Your reticulocyte count is low. That tells your doctor your bone marrow isn’t making red blood cells fast enough.
- Hemolytic anemia: Your reticulocyte count is high. This type of anemia destroys red blood cells before they would normally die, so your bone marrow has to work overtime to replace them.
- Iron deficiency anemia: A low reticulocyte count also can be a sign of this. It happens when your body doesn’t have enough iron to make red blood cells.
- Pernicious anemia: Your body doesn’t get enough vitamin B12, also producing a low reticulocyte count.
Other Reasons to Get One
A reticulocyte count test is also useful for people with sickle cell disease. That’s a disorder that makes your body produce red blood cells that are shaped like a crescent, or sickle, instead of being round.
Sickle cells die early and can caught in blood vessels, forming obstructions that cut off circulation to parts of the body. They can cause a form of anemia, because there aren’t enough healthy red blood cells to carry oxygen, as well as other painful or life-threatening illnesses that can put you in the hospital. A high reticulocyte count in someone with sickle cell disease suggests increased hemolysis, and points to a sickle cell crisis. Sickle cell crisis is usually painful and can be life-threatening.
Doctors also use reticulocyte counts when someone has had:
- Chemotherapy or radiation treatment for cancer
- A bone marrow transplant
- Other conditions that can affect production of red blood cells
The tests can tell your doctor whether your bone marrow is starting to recover from the treatment.