What is Mean Corpuscular Hemoglobin (MCH)?

MCH Gives Clues as to Causes of Anemia

Red Blood Cells within a Blood Vessel. Credit: Oliver Cleve / Getty Images

Mean corpuscular hemoglobin (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. 

Understanding Your MCH Value

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?

When your MCH is low, you may have iron-deficiency anemia. This type of anemia can be caused by insufficient iron in the diet, by blood loss, or disorders in being able to absorb, store or use iron in your body. 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 MCV.

High MCH levels may indicate the presence of a macrocytic anemia and can have a variety of causes, including liver disease, and deficiencies of vitamin B12 and folic acid (folate). This can also be seen during chemotherapy.

You can still be anemic and have a normal MCH though. This may occur with sudden blood loss, chronic illnesses, tumors, blood infections and in kidney failure.

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 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.

Sources:

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

Martin LJ. U.S. National Libray of Medicine: Medline Plus.  (?March 2016). RBC indices

Van Vranken M. Evaluation of Microcytosis, Am Fam Physician. 2010 Nov 1;82(9):1117-1122.

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