What Are Red Blood Cell Indices?

Values help pinpoint underlying cause of anemia

red and white blood cells
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The complete blood count (CBC) is a blood test ordered by doctors so that they can evaluate the composition and quality of the blood cells in your body. These blood cells include:

  • White blood cells (leukocytes) which help fight infection
  • Red blood cells (erythrocytes) which distribute oxygen throughout the body
  • Platelets (thrombocytes) which clot blood

In addition, the CBC includes an evaluation known as the red blood cell indices (or RBC indices).

The RBC indices provide information about the size and quality of your red blood cells. This can be used to diagnose the cause and severity of anemia and provide vital clues about other health conditions you may have.

The RBC indices are comprised of three different components known as the mean corpuscular hemoglobin concentration (MCHC), the mean corpuscular volume (MCV), and the 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.

Hemoglobin is the iron-carrying protein in red blood cells whose function it is to carry oxygen. It is also the element that gives red blood cells their color. Any alternation in concentration can cause the cells to appear more or less red.

The MCHC basically tells you whether a person's red blood cells have more or less hemoglobin than what would be expected.

A normal range for MCHC is between 33.4 and 35.5 grams per deciliter in adults. Any value outside of the reference range is defined as follows:

  • When the MCHC is high, the cells are referred to as being hyperchromic. Two possible causes for this are autoimmune hemolytic anemia (in which the immune system attacks its own blood cells) and hereditary spherocytosis (a genetic disorder characterized by anemia and gallstones). Both are considered rare.
  • When the MCHC, the cells are referred to as being hypochromic. This commonly occurs with iron deficiency anemia and results in less oxygen being delivered to cells and tissues. Any number of conditions can cause iron deficiency anemia, including pregnancy, blood loss, poor iron absorption in the gut (caused, for example, with Celiac disease or Crohn's disease), and poor nutritional intake of iron.

Whether hyperchromic or hypochromic, treatment is primarily focused on treating the underlying condition. Iron supplementation and the increased dietary of intake of iron can help treat iron deficiency anemia. Blood transfusions may be used in more severe cases.

Mean Corpuscular Volume (MCV)

Mean corpuscular volume (MCV) measures the average red blood cell volume, meaning the actual size of the cells themselves. A normal range for MCV is between 80 and 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 (again) is iron deficiency anemia. Other possible causes include lead poisoning, thalassemia (a genetic disorder characterized by abnormal hemoglobin production) and anemia related to chronic diseases such as rheumatoid arthritis or giant cell arteritis.
  • A high MCV implies the red blood cells are larger than normal, or macrocytic. Causes of macrocytic anemia include vitamin B12 deficiency, folate deficiency, liver disease, alcoholism, hypothyroidism, and certain drugs (including those used for cancer chemotherapy and to treat HIV).

It's important to note that a person can have anemia and have a normal MCV. This is called a normocytic anemia. Causes are similar to that other form of anemia and may include sudden blood loss, kidney failure, hemolytic anemia, and nutritional deficiency.

Mean Corpuscular Hemoglobin (MCH)

Mean corpuscular hemoglobin (MCH) is the average amount of hemoglobin per red blood cell in a sample of blood.

A normal range for MCH is between 27.5 and 33.2 picograms per cell.

The MCH value directly parallels the MCV value. As such, if the size of the red blood cells is large (as measured by the MCV), the amount of hemoglobin per red blood cells will be high (as measured by the MCH), and vice versa.

While the MCH can be used alone to determine if the anemia is hyper-, hypo-, or normocytic, the MCV has to be considered along with the MCH since the cell volume directly affects the content of hemoglobin per cell.

A Word From Verywell

A CBC is a standard blood test, and understanding what the values mean allows you to take a more active role in your health. However, try not to get too bogged down in the specifics but rather how the values compared to the normal (reference) range.

In the end, your CBC is one of several tests used to diagnose the underlying cause of anemia and other medical conditions.

If any of the CBC values are outside of the reference range, don’t be afraid to ask your doctor what that means. The more you take part, the more you can make informed decisions about your health.

Sources:

DeLoughery, T. “Microlytic Anemia.” N Engl J Med. 2014; 371:1324-1331; DOI 10.1056/NEJMra1215361.

Moreno Chulilla, J.; Romero Colás, M.; ad Gutiérrez Martin, M. “Classification of anemia for gastroenterologists.” World J Gastroenterol. 2009; 15(37):4627-37; DOI 10.3748/wjg.15.4627.

Nagao, T. and Hirokawa, M. “Diagnosis and treatment of macrocytic anemia ​in adults.” J Gen Fam Med. 2016; 1-5; DOI 10.1002/jgf2.31.

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