Learn Exactly What Red Blood Cell Indices Can Tell You

RBC Values help pinpoint causes of anemia and other diseases

red and white blood cells
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If you are looking at your red blood cell count on a complete blood count (CBC), you may see a number of different initials included along with the total count. The red blood cell indices, called MCHC, MCV, MCH, and RDW give further information about your red blood cells and can be helpful in determining the cause of anemia and other medical conditions.

Let's take a look at the information contained in your CBC) including your red blood cell count, and then discuss the meaning and importance of each of these indices.

Your Complete Blood Count (CBC)

The complete blood count (CBC) is a blood test ordered by your doctor to 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

Red Blood Cell Count (RBC)

The red blood cell count (RBC) is the number of red blood cells that are found in your blood. A normal RBC count depends on age and gender:

  • For women, 4.2 - 5.4 million/mcL
  • For men, 4.7 - 6.1 million/mcL
  • For children 4.1 - 5.5 million/mcL

A low red blood cell count is referred to as anemia. There are many different causes of anemia, of which iron deficiency is only one. Red blood cell indices are very helpful in distinguishing these different causes.

An elevated red blood cell count is called erythrocytosis or polycythemia. Causes may include dehydration (in which the level isn't actually high, but appears that way due to less fluid volume in the blood), a need for greater oxygen carrying capacity of the blood, such as living at high altitudes, COPD, or heart failure, and an increased production of red cells in the bone marrow due to conditions such as polycythemia vera.

While looking at the total RBC count can tell you if your number of red blood cells is low, normal, or high, it doesn't tell you why the count is abnormal. Hence the need for further evaluation of these cells. Even if the RBC count is normal, looking at the RBC indices can sometimes give important clues in diagnosing medical conditions.

Red Blood Cell (RBC) Indices 

Along with the total RBC count, 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 four different components known as the mean corpuscular hemoglobin concentration (MCHC), the mean corpuscular volume (MCV), the mean corpuscular hemoglobin (MCH), and the red cell distribution width (RDW).

Mean Corpuscular Hemoglobin Concentration (MCHC)

The 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:

High MCHC

When the MCHC is high, the red cells are referred to as being hyperchromic. Possible causes of a high MCHC (which is uncommon) include:

  • Autoimmune hemolytic anemia, a condition in which the bodies immune system attacks its own red blood cells
  • Hereditary spherocytosis, a genetic condition characterized by anemia and gallstones

Low MCHC

When the MCHC is low, the cells are referred to as being hypochromic. Possible causes include:

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, but an iron supplement is not recommended for people who are not iron deficient (excess iron can be stored in the liver and heart). 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.

Low MCV

A low MCV indicates that the red blood cells are small, or microcytic. Possible causes include:

  • Lead poisoning
  • Thalassemia (the thalassemias are genetic disorders characterized by abnormal hemoglobin)
  • Anemia of chronic disease
  • Rheumatoid arthritis
  • Giant cell arteritis.

High MCV

A high MCV implies the red blood cells are larger than normal, or macrocytic. Causes of macrocytic anemia include:

  • Vitamin B12 deficiency
  • Folate deficiency (both vitamin B12 deficiency and folate deficiencies are also called megaloblastic anemia, due to the macrocytic RBCs)
  • Liver disease
  • Alcoholism
  • Hypothyroidism
  • Medications such as chemotherapy drugs and retroviral therapies for HIV

Normal MCV

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

  • Sudden blood loss
  • Kidney failure
  • Hemolytic anemia
  • Nutritional deficiencies

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, and some physicians find that the test is redundant. 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.

Red Cell Distribution Width (RDW)

Red cell distribution width (RDW) is a test which reflects the variability in size of the red blood cells (and is proportionate the standard deviation of the MCV). A normal RDW would mean that the red blood cells are all similar in size, whereas a higher RDW means that there is more variability in size of the red blood cells.

Some physicians believe that RDW is one of the most helpful red cell indices in making diagnoses. Aside from its role in helping to diagnose anemia, an elevated RDW may predict the presence of coronary artery disease in people with high blood pressure. It also provides clues to an early nutritional deficiency which may not be noted with the other tests alone. Finally, it a good test for determining if further testing is needed, such as a peripheral blood smear.

A normal range for RDW is 10.2 to 14.5 percent.

RDW is most helpful when evaluated along with MCV. An example of some causes include:

High RDW and low MCV (microcytic):

  • Iron deficiency anemia
  • Sickle cell anemia

High RDW and normal MCV (normocytic):

  • Iron deficiency anemia
  • Combined anemias
  • Hemorrhage (a few days later)
  • Hemoglobin variants

High RDW and high MCV (macrocytic):

  • Vitamin B12 deficiency
  • Folate deficiency
  • Cold agglutinin disease
  • Myelodysplastic syndrome
  • Immune hemolytic anemia

Normal RDW and high MCV:

  • Liver disease (chronic)
  • Aplastic anemia
  • Alcohol-related

Normal RDW and low MCV:

  • Anemia of chronic disease
  • Some types of thalassemia
  • Some abnormal hemoglobins

It's important to note that these are only a few examples, and there are many possibilities.

A Word From Verywell

A CBC is a standard blood test and includes the red blood cell count in addition to white blood cell count and platelets. The red blood cell count can tell doctors about the number of red blood cells you have but says little about the reason for any abnormalities.

RBC indices, by looking at the characteristics of red blood cells, are helpful in not only figuring out the cause of an anemia but in diagnosing medical conditions even when the red blood cell count is normal.

The combination of these indices also gives important clues in narrowing down an anemia. The examples given above are only a few of the possible causes, and determining the precise cause of anemia is sometimes very challenging. These blood tests are best used in combination with a careful history, a thorough physical exam, and any imaging tests which are indicated.

Learning about these blood tests can help you ask your doctor questions so that you thoroughly understand either a diagnosis she has made, or further testing she is recommending. Increasingly, people are being called on to be an active participant in their health care, and learning how to make informed decisions about their health. Taking the time to learn about your lab values can help you be empowered in making the choices that are best for you alone.

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