Red blood cell (RBC) indices measure your RBCs’ shape, size, and physical characteristics. They are part of a complete blood count (CBC) test. It can help diagnose conditions like anemia.

Your blood consists of various components suspended in plasma. These include:

  • red blood cells (RBCs), which contain hemoglobin and carry oxygen to all your tissues and organs
  • white blood cells (WBCs), which are immune cells that help protect your body from infection
  • platelets, which are cells that enable clot formation

An RBC is pale red and gets its color from hemoglobin. It’s shaped like a doughnut but has a thinner area in the middle instead of a hole. RBCs are typically all the same color, size, and shape. However, certain conditions can cause variations that impair their ability to function properly.

A doctor can use RBC indices to help diagnose various blood disorders, including anemia. Anemia is a common blood disorder that affects the shape or number of your RBCs and, as a result, their function.

Continue reading to learn more about RBC indices, including why doctors order them, what they measure, and what the results mean.

RBC indices and RBC count are tests used to diagnose different forms of anemia. If you have a low RBC count or abnormal RBC indices, you may have anemia.

Anemia is a condition in which the number of RBCs or the amount of hemoglobin in your blood falls below normal levels. Having anemia means that your RBCs are not able to deliver the appropriate amount of oxygen to your organs and tissues.

Anemia can occur if:

Types of anemia

Doctors may use the following words to describe different types of anemia, depending on how it develops:

  • Inherited: Anemia can be a genetic condition passed down from parents to children.
  • Acquired: Anemia can also develop during your life due to other health conditions or environmental factors.
  • Acute: Anemia can be acute, meaning it develops over a short period.
  • Chronic: Anemia can also be chronic, which means it develops and persists over months to years.
  • Idiopathic: Anemia may have an unknown cause.

Causes of anemia

Possible causes of anemia include:

  • nutritional deficiencies, such as diets lacking in iron, vitamin B12, or folate
  • chronic diseases like cancer, diabetes, inflammatory bowel disease (IBD), kidney disease, or thyroiditis (inflammation of the thyroid gland)
  • chronic infections like human immunodeficiency virus (HIV) or tuberculosis
  • significant blood loss
  • diseases affecting the bone marrow, such as leukemia, lymphoma, or multiple myeloma
  • chemotherapy
  • lead poisoning
  • pregnancy
  • 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.

Symptoms of anemia

If you have anemia, the symptoms can be mild at first. Some people may not have symptoms and only find out they have anemia from a blood test. Common symptoms may include:

  • fatigue
  • lack of energy
  • weakness
  • pale skin

As anemia progresses, symptoms may include:

  • dizziness
  • a feeling of cold or numbness in your hands and feet
  • shortness of breath
  • irregular or fast heartbeat
  • chest pains
  • headaches
  • brittle nails

Most people don’t know they have anemia until they have a routine CBC blood test.

The CBC is a broad test that measures the number of all RBCs, WBCs, and platelets in a blood sample. If a CBC shows you have anemia, the RBC and the RBC indices can help to determine what’s causing it.

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:

  1. If the blood is taken from a vein inside your elbow, a healthcare professional first cleans the test area with an antiseptic and wraps an elastic band around your upper arm to make the vein swell.
  2. A needle is gently inserted, and blood flows into a tube.
  3. When the tube is filled, the healthcare professional removes the elastic band and then removes the needle.
  4. A bandage may be placed over the area where the needle was inserted.
  5. The sample is then sent to a laboratory for analysis.

The RBC indices have three parts:

  • mean corpuscular volume (MCV), which is the average red blood cell size
  • mean corpuscular hemoglobin (MCH), which is the average amount of hemoglobin per red blood cell
  • mean corpuscular hemoglobin concentration (MCHC), which is the average amount of hemoglobin relative to the size of the cell or hemoglobin concentration per red blood cell

The normal ranges for RBC indices may vary slightly from lab to lab.

The normal values for RBC indices in adults may include:

  • MCV: 80 to 100 cubic micrometers (µm3)
  • MCH: 27 to 32 picograms per cell (pg/RBC)
  • MCHC: approximately 34% hemoglobin per cell (Hb/cell)

The RBC indices can help your doctor determine the cause of anemia if your doctor thinks you have it. The MCV is the most useful value in the RBC indices to help determine the type of anemia you may have.

Your doctor will check your MCV to determine whether it is low, normal, or high to help determine what is causing your anemia.

High MCV

When red blood cells are larger than normal, the MCV is higher than normal. This is called macrocytic anemia.

Macrocytic anemia can result from:

Low MCV

When red blood cells are too small, the MCV is lower than normal. This condition is called microcytic anemia.

Microcytic anemia may be caused by:

Normal MCV

If you have a normal MCV, 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. 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 disorder in which the bone marrow stops making new blood cells
  • a blood infection

High MCHC

If you have a high MCHC, the relative hemoglobin concentration per red blood cell is high. MCHC can be elevated in diseases such as:

Low MCHC

If you have a low MCHC, 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
  • thalassemia
  • lead poisoning

Low MCV and MCHC generally occur together. Anemias in which both MCV and MCHC are low are called microcytic hypochromic anemia.

Your doctor may also perform other tests before making a diagnosis.

This can help them accurately diagnose and treat the underlying cause of your anemia.

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 causing anemia, treatment for that disease can often also improve the anemia.

RBC indices are blood tests that help doctors measure your red blood cells’ number, size, shape, and other characteristics.

It can help doctors diagnose anemia and its possible underlying cause.

If you’re experiencing any of the symptoms of anemia or have any concerns about the results of your CBC or RBC indices, it’s best to talk with your doctor.