What is Mean Corpuscular Hemoglobin (MCH)?

MCH Gives Clues as to Causes of Anemia

Red Blood Cells within a Blood Vessel
What is mean corpuscular hemoglobin (MCH) and how does this help physicians diagnose types of anemia?. Credit: Oliver Cleve / Getty Images

When you have your blood count tested, you will see many abbreviations which give further information about your red blood cells. One of these "red blood cell indices" is MCH. MCH stands for mean corpuscular hemoglobin and can give important information in diagnosing anemia. What is the definition of MCH, why is this test done, and what might it mean if the number is abnormal?

Mean Corpuscular Hemoglobin (MCH): Definition

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

MCH is used to help diagnose the type, cause, and severity of anemia. You will see the MCH reported as part of a complete blood count (CBC) test—a common blood draw. Red blood cell indices and other numbers which describe red blood cells include:

Understanding Your Mean Corpusclular Hemoglobin (MCH) Value

The MCH is an important test in figuring out the amount of hemoglobin in your red blood cells. There are many causes of anemia, which are broken down into three basic categories:

  • Normochronic
  • Hypochromic
  • Hyperchromic

The normal range for MCH is 27-31 picograms/cell in adults. This is known as normochromic, meaning your red blood cells are of a normal size. 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.

A low MCH is known as hypochromic because there is less hemoglobin in the red cells, which give them their red color. In this case, the red blood cells appear paler.

 A high MCH with anemia is known as hyperchromic anemia.

What Do High or Low MCH Values Mean?

Let's look at what it might mean if your MCH is high, low, or normal.

Low MCH - When your MCH is low, you may have iron-deficiency anemia. Iron-deficiency anemia can be caused by insufficient iron in the diet, by blood loss, or disorders in your body's ability to absorb, store or use iron. Blood loss, such as what might occur with tumors in the colon and other parts of gastrointestinal tract, can also cause low iron levels, resulting in smaller red blood cells that have less hemoglobin, with a low mean corpuscular volume (MCV.)

High MCH - High MCH levels may indicate the presence of a macrocytic anemia and can have a variety of causes, including:

  • Liver disease
  • Vitamin B12 deficiency
  • Folic acid deficiency
  • Chemotherapy

Normal MCH - You can have a normal MCH and still be anemic. Some types of conditions which may have a normal MCH (normochromic) index include:

In addition to helping determine the type of anemia, MCH may be used to predict prognosis as well. For example, in the setting of a heart attack a low MCH may predict poorer outcomes than for people with a normal MCH.

MCV provides similar information to MCH, and overall, MCV and RDW are used more often than MCH in evaluating the causes of anemia.

How the MCH Test is Performed

The MCH is a typical part of the complete blood count test. First, your blood is drawn in a tube that contains an anticoagulant to keep the sample from clotting. A small sample is then analyzed by a Coulter counter that sends the cells through an aperture where they are counted and their size is measured. The amount of hemoglobin is measured after bursting the red cells. Then the instrument does a math computation of the hemoglobin weight divided by the red blood cell count.

If a blood count differential is also ordered, the lab technologists will make a slide of your blood, stain it and examine it under a microscope. The lab technologists can see the color of your red blood cells, which is directly due to the amount of hemoglobin in each of them. This visual assessment is used to confirm what the analyzer measured.

Your MCH value should not change rapidly, as it takes more than a few days for your body to produce differently sized red cells. That being said, it may change if you received a transfusion. Changes other than those due to a transfusion will lead to suspicion that the sample was mislabeled or mishandled, and the lab will usually request a repeat sample rather than report the result.

Summary of Mean Corpuscular Hemoglobin

There are many different types of anemia with varying causes. An MCH is an important test in breaking down the causes of anemia. That said, a diagnosis of anemia is usually made by looking at the results of your blood counts as a whole, such as your red blood cell count, your hemoglobin, your mean corpuscular volume, your red blood cell distribution width (RDW) and visual assessment of your smear. These tests are looked at in combination with clinical information from your history and physical, other laboratory tests, and possibly imaging studies.

The red blood cell indices MCV and RDW are used more often to evaluate the causes of anemia, but MCH can be a helpful adjunct, especially when looked at in comparison to MCV. It may also be helpful in predicting the prognosis of someone who is very ill.

Sources:

Buttarello, M. Laboratoy Diagnosis of Anemia: Are the Old and New Red Cell Parameters Useful in Classification and Treatment, How?. International Journal of Laboratory Medicine. 2016. 38 Suppl 1:123-32.

Green, R., and D. Dwyre. Evaluation of Macrocytic Anemias. Seminars in Hematology. 2015. 52(4):279-86.

Huang, Y., and H. Hu. Lower Mean Corpuscular Hemoglobin Concentration is Associated with Poorer Outcomes in Intensive Care Unit Admitted Patients with Acute Myocardial Infarction. Annals of Translational Medicine. 2016. 4(10):190.

Kasper, Dennis L.., Anthony S. Fauci, and Stephen L.. Hauser. Harrison's Principles of Internal Medicine. New York: Mc Graw Hill education, 2015. Print.

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