What Are Red Blood Cell Indices?

Values measured on a complete blood count that describe your anemia

Red blood cell size and colors can provide insight into your anemia.
Susumu Nishinaga/Science Photo Library / Getty Images

The complete blood count, or CBC, is a blood test ordered by your doctor so he can examine the cells traveling through your bloodstream. These cells include:

  • white blood cells (your infection-fighting cells)
  • red blood cells (contain hemoglobin, which are the carriers of oxygen throughout your body)
  • platelets (your clotting cells)

In addition to providing a count of the red blood cells in your bloodstream, a CBC also provides something called red blood cell indices, or RBC indices.

RBC indices provide information about the size and color of your red blood cells. This information can help a doctor diagnose the cause and severity of your anemia, if present, as well as provide clues about other health conditions you may have.

What Are the Red Blood Cell Indices?

The three red blood cell indices measured on a complete blood count include:

  • mean corpuscular hemoglobin concentration (MCHC)
  • mean corpuscular volume (MCV)
  • mean corpuscular hemoglobin (MCH)

Mean Corpuscular Hemoglobin Concentration (MCHC)

A mean corpuscular hemoglobin concentration (MCHC) is the average concentration of hemoglobin in red blood cells. It basically tells you whether a person's red blood cells pack in more or less hemoglobin than usual. This results in the red cells appearing more or less red, as hemoglobin is what gives them their color.

A normal range for MCHC is 33.4 to 35.5 grams per deciliter in adults.

When the MCHC is low, it means there is less hemoglobin in each red cell, regardless of the size of the red cell. In this case, the red blood cells are termed hypochromic because they are pale. Hypochromic red blood cells are seen in people with iron deficiency anemia or thalassemia.

In iron deficiency anemia, there is not enough iron in the body to make hemoglobin—as a result, cells are small.

There are multiple ways in which a person can develop iron deficiency anemia. Common causes include:

  • pregnancy (increased demand for iron)
  • chronic blood loss (for example, heavy menstruation in women or a from a tumor in the colon)
  • poor iron absorption in the gut (for example, Celiac disease or Crohn's disease)
  • poor nutritional intake of iron

Fixing the underlying problem (for example, eliminating gluten if you have Celiac disease) and supplementing with iron tablets and/or eating iron-rich foods (lean meats, seafood, and beans) can usually reverse an iron deficiency anemia and normalize the MCHC on a CBC.

When the MCHC is high, the cells are hyperchromic, as there is a higher concentration of hemoglobin in each red cell than is normal. Two examples of a health condition in which the MCHC is high (which is rather rare) include:

  • autoimmune hemolytic anemia: a disorder in which a person's own immune system destroys their red blood cells
  • hereditary spherocytosis: a disorder that a person is born with and can cause anemia and gallstones

Mean Corpuscular Volume (MCV)

Mean corpuscular volume (MCV) measures the average red blood cell volume—in other words, the size of the red blood cells. A normal range for MCV is 80 to 96 femtoliters per cell.

A low MCV indicates that the red blood cells are small, or microcytic. The most common cause of a microcytic anemia is iron deficiency anemia.  

Other causes of a microcytic anemia include lead poisoning, thalassemia, and anemia of chronic diseases (for example, a person with rheumatoid arthritis or giant cell arteritis).

A high MCV implies the red blood cells are larger than normal—this is called a macrocytosis. Examples of health conditions that cause a macrocytic anemia include:

Certain medications like types of chemotherapies or HIV treatments can cause a macrocytosis, as well.

It's important to note that a person can have anemia and have a normal MCV. This is called a normocytic anemia. Causes of a normocytic anemia include:

  • sudden blood loss
  • kidney failure
  • having a chronic disease (called "anemia of chronic disease")
  • hemolytic anemia
  • nutritional anemia (often a combination of vitamin B12, folate, and iron)

Mean Corpuscular Hemoglobin

Mean corpuscular hemoglobin (MCH) is the average amount of hemoglobin per red blood cell in a blood sample. A normal range for MCH is 27.5 to 33.2 picograms per cell—this is referred to as normochromic.

The MCH is usually either high or low if the size of your red blood cells (measured by the MCV) is high or low. Bigger red blood cells usually have more hemoglobin and smaller red blood cells usually have less hemoglobin, simply due to their size. The big picture here is that the MCH value reflects the value of the MCV.

A Word From Verywell

A complete blood count is a common blood test, and understanding what the values mean, including those of the red blood cell indices, allow you to take a more active role in your blood health. That being said, try not to get too bogged down into the nitty gritty meaning behind each number.

Remember, your CBC is simply one test (usually the first test) to provide a clue to the cause of your anemia. Your doctor will likely need other blood tests or even a colonoscopy, imaging test, or bone marrow biopsy to confirm the diagnosis.

Continue to follow closely with your doctor, ask questions if your CBC has any abnormal results, and of course, speak with your doctor if you are worried you are experiencing any symptoms of anemia.

Sources:

American Association for Clinical Chemistry. (March 2017). Labs Test Online: Complete Blood Count.

Moreno Chulilla JA, Romero Colás MS, Gutiérrez Martín M. Classification of anemia for gastroenterologists. World J Gastroenterol. 2009 Oct 7;15(37):4627-37.

Kaferle J, Strzoda CE. Evaluation of macrocytosis. Am Fam Physician. 2009 Feb 1;79(3):203-08.

Martin LJ. (March 2016). U.S. National Library of Medicine: RBC Indices.

Van Vranken M. Evaluation of microcytosis. Am Fam Physician. 2010 Nov 1;82(9):1117-22.

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