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Red blood cell (RBC) indices are individual components of a routine blood test called the complete blood count (CBC). The CBC is used to measure the quantity and physical characteristics of different types of cells found in your blood.
Blood consists of RBCs, white blood cells (WBCs), and platelets that are suspended in your plasma. Platelets are cells that enable clot formation. RBCs contain hemoglobin, which carries oxygen throughout your body to all of your tissues and organs. An RBC is pale red and gets its color from hemoglobin. It’s shaped like a doughnut, but it has a thinner area in the middle instead of a hole. Your RBCs are normally all the same color, size, and shape. However, certain conditions can cause variations that impair their ability to function properly.
The RBC indices measure the size, shape, and physical characteristics of the RBCs. Your doctor can use RBC indices to help diagnose the cause of anemia. Anemia is a common blood disorder in which you have too few, misshapen, or poorly functional RBCs.
Your RBC indices and RBC count are used to diagnose different types of anemia. You have some form of anemia if you have a low RBC count or abnormal RBC indices.
Anemia is a condition in which the number of RBCs or the amount of hemoglobin in your blood falls below normal levels. This deprives tissues throughout your body of oxygen. You may feel fatigued, lightheaded, short of breath, or have other symptoms if your body doesn’t get all the oxygen it requires to function properly.
Anemia can occur if:
Anemia has many different causes. It can be inherited, which means it’s a genetic condition passed down from parents to children through their genes. Anemia can also develop sometime during your life. Anemia can be acute, meaning it develops over a short period of time. Anemia can also be chronic, meaning it develops and persists over months to years.
Possible causes of anemia include:
Iron deficiency anemia is the most common kind of anemia.
The symptoms of anemia can be very mild at first. Many people aren’t even aware that they’re anemic. The most common early symptoms of anemia include:
As the disease progresses, your symptoms may include:
Most people don’t know they have anemia until they have a CBC, which is a routine blood test. The CBC is a broad test that measures the number of all RBCs, WBCs, and platelets in a sample of blood. If you’re found to have anemia, the RBC and the RBC indices can help to determine what’s causing your anemia.
The test for RBC indices involves taking a small sample of blood. You don’t need to prepare for the test. The following steps describe what happens:
The RBC indices has three parts:
According to the American Association for Clinical Chemistry, normal values for RBC indices are:
Normal ranges may vary slightly from lab to lab.
The RBC indices can help your doctor determine the cause if your doctor thinks you have anemia. The MCV is the most useful value in the RBC indices to help determine the type of anemia you may have.
Your doctor will see if your MCV is low, normal, or high to help determine what is causing your anemia.
The MCV is higher than normal when red blood cells are larger than normal. This is called macrocytic anemia.
Macrocytic anemia can be caused by:
The MCV will be lower than normal when red blood cells are too small. This condition is called microcytic anemia.
Microcytic anemia may be caused by:
If you have a normal MCV, it means that your red blood cells are normal in size. You can have a normal MCV and still be anemic if there are too few red blood cells or if other RBC indices are abnormal. This is called normocytic anemia.
Normocytic anemia occurs when the red blood cells are normal in size and hemoglobin content, but there are too few of them. This can be caused by:
If you have a high MCHC, this means that the relative hemoglobin concentration per red blood cell is high. MCHC can be elevated in diseases such as:
If you have a low MCHC, it means that the relative hemoglobin concentration per red blood cell is low. The red blood cells will take on a lighter color when viewed under the microscope. Individuals with anemia and a corresponding low MCHC are said to be hypochromic. Conditions that can cause low MCHC include the same conditions that cause low MCV, including:
Generally, a low MCV and a MCHC will be found together. Anemias in which both MCV and MCHC are low are called microcytic, hypochromic anemia.
Your doctor may also perform other tests to make a diagnosis. Treatment for any anemia depends on the underlying cause. For example, if your anemia is caused by iron deficiency, your doctor may advise you to take iron supplements or change your diet to include more foods that are rich in iron. If you have an underlying disease that’s causing anemia, treatment for that disease can often also improve the anemia.
Talk to your doctor if you’re experiencing any of the symptoms of anemia or if you have any concerns about the results of your CBC or RBC indices.
Written by: Judith Epstein and Jacquelyn Cafasso
Medically reviewed on: Apr 10, 2017: Deborah Weatherspoon, PhD, RN, CRNA
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