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:
- too few RBCs are created, which is called aplastic anemia
- RBCs are destroyed prematurely, which is called hemolytic anemia
- a significant blood loss occurs, such as in cases of hemorrhage.
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:
- diets lacking in iron, vitamin B-12, folate, or folic acid
- chronic diseases like cancer, diabetes, inflammatory bowel disease, kidney disease, or thyroiditis, which is an inflammation of your thyroid gland
- chronic infections like HIV or tuberculosis
- significant blood loss or hemorrhage
- diseases affecting your bone marrow, such as leukemia, lymphoma, or multiple myeloma
- lead poisoning
- certain genetic diseases, such as thalassemia, which is an inherited form of anemia, or sickle cell disease, which occurs when your RBCs can’t carry oxygen well because they’re sickle-shaped
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:
- lack of energy
- pale skin
As the disease progresses, your symptoms may include:
- a feeling of cold or numbness in your hands and feet
- shortness of breath
- irregular or fast heartbeat
- chest pains
- brittle nails
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:
- If the blood is taken from a vein inside your elbow, a healthcare provider will first clean the test area with an antiseptic and wrap an elastic band around your upper arm to make the vein swell.
- A needle is gently inserted, and blood flows into a tube.
- When the tube is filled, the healthcare provider removes the elastic band and then removes the needle.
- A bandage may be placed over the area where the needle was inserted.
- The sample is then sent to a laboratory for analysis.
The RBC indices has three parts:
- mean corpuscular volume (MCV), which is the average red blood cell size
- mean corpuscular hemoglobin (MCH), which is the amount of hemoglobin per red blood cell
- mean corpuscular hemoglobin concentration (MCHC), which is the amount of hemoglobin relative to the size of the cell or hemoglobin concentration per red blood cell
According to the American Association for Clinical Chemistry, normal values for RBC indices are:
- The MCV should be 80 to 96 femtoliters.
- The MCH should be 27 to 33 picograms per cell.
- The MCHC should be 33.4 to 35.5 grams per deciliter.
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:
- Vitamin B-12 deficiency
- folate deficiency
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:
- iron deficiency, which can be caused by poor dietary intake of iron, menstrual bleeding, or gastrointestinal bleeding
- lead poisoning
- chronic diseases
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:
- a sudden and significant blood loss
- a prosthetic heart valve
- a tumor
- a chronic disease, such as a kidney disorder or endocrine disorder
- aplastic anemia
- a blood infection
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:
- hereditary spherocytosis
- sickle cell disease
- homozygous hemoglobin C disease
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:
- iron deficiency
- chronic diseases
- lead poisoning
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.
After the test
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.