Mean Corpuscular Hemoglobin (MCH)

What is mean corpuscular hemoglobin (MCH)?

Mean corpuscular hemoglobin, or MCH, is a value on a routine blood test called a complete blood count (CBC). It measures the average (“mean”) amount of hemoglobin you have per red blood cell. Hemoglobin is an essential protein in your red blood cells that allows them to do their main job: Carry oxygen throughout your body. The oxygen powers your cells and keeps your body functioning.

MCH is just one value on a complete blood count that provides information about your red blood cells. This part of the CBC is called the RBC indices. Other values on the RBC indices include:

• Mean corpuscular volume (MCV): Measures the average size of your red blood cells.
• Mean corpuscular hemoglobin concentration (MCHC): Measures the average amount of hemoglobin concentration per red blood cell. (Unlike MCH, MCHC factors in both the amount of hemoglobin per red blood cell and the sizes of your RBC.)
• Red blood cell distribution width (RDW): Measures how varied in size your RBCs are.

These details about your RBC allow providers to diagnose health conditions, especially anemia.

When is MCH on a blood test needed?

MCH is a standard part of a CBC, which checks the health of your red blood cells, white blood cells and platelets. MCH — like all values on a CBC — helps healthcare providers catch signs of a condition early.

MCH values are especially useful for your provider to know about if you have symptoms of anemia, like fatigue or frequent headaches. Considered alongside the other RBC indices, an abnormal MCH can help your provider determine whether you have anemia. It can also help them determine what’s likely causing it.

How does the test work?

Testing for MCH involves a simple blood draw. A provider (usually a nurse or phlebotomist) will collect a sample of your blood. Afterward, they’ll run it through an automated blood counter that analyzes the sample and provides information about your blood cells.

The blood analysis of your red blood cells in particular calculates MCH.

How do I prepare?

You don’t need to do anything special to prepare for getting your MCH checked. If your provider plans to run additional tests on your blood sample, you may need to fast (no food or drink) beforehand. Follow the instructions your provider gives you to prepare so you’re ready.

What to expect during the test?

You’ll be seated for the blood draw with your arm extended. A provider will:

1. Clean the injection site with an alcohol wipe.
2. Tie a rubber band above the site so more blood collects at the spot where they’ll take the sample.
3. Gently insert a needle at the injection site. Blood will flow quickly into a vial or collection tube.
4. Remove the needle and secure a cotton ball at the site to stop the bleeding.

The procedure is quick (usually five minutes or less) and painless. At most, you may feel a quick sting when the needle goes in.

What to expect after the test?

You’ll get to leave shortly after giving blood unless you’re feeling light-headed. Some people feel woozy around blood, no matter how painless the procedure. If this sounds like you, you’re not alone. Your provider will monitor you to ensure you’re feeling better before you go.

What are the risks of this test?

The test to determine your MCH (a CBC) isn’t risky. After you give blood, you may notice a small bruise where the needle went in, and your arm may be sore at first. But these symptoms usually go away the same day of your blood draw.

What type of results do you get and what do they mean?

MCH results show the average number of picograms (a picogram is one-trillionth of a gram) of hemoglobin you have per red blood cell (pg/cell). Although labs vary, the normal MCH range is between 27 and 33 pg/cell for adults, regardless of sex. Amounts below this range are considered low MCH. Amounts above are high (elevated) MCH.

Keep in mind that a high or low result isn’t necessarily cause for concern. Your provider will consider your MCH alongside the other RBC indices to see if there’s an issue or to determine if you need additional tests.

Low MCH

A low MCH may mean that you may have hypochromic anemia (when your red blood cells are paler than normal) and/or microcytic anemia (when your red blood cells are abnormally small). With both conditions, your red blood cells don’t have enough hemoglobin.

Causes of low MCH include:

• Iron deficiency: Having too little iron can prevent your body from making enough hemoglobin. The most common cause of iron-deficiency anemia is blood loss. It can happen because of heavy period bleeding, internal bleeding or excessive bleeding after surgery.
• Hemoglobinopathies: Some blood disorders can cause problems with how your body makes hemoglobin. Examples include thalassemia and sickle cell anemia.
• Inflammation associated with chronic (long-term) conditions: Long-term infections, kidney disease, liver disease and cancer can lead to inflammation that causes low MCH.

High MCH

A high MCH may mean that you have macrocytic anemia. With macrocytic anemia, your body produces abnormally large red blood cells that contain high levels of hemoglobin. Often, it happens because your body isn’t getting enough of the key ingredients needed to make healthy RBCs: folate and B12. Or you have a condition that prevents your body from absorbing these nutrients.

Causes of elevated MCH include:

• Long-term alcohol use disorder.
• Problems with your thyroid gland.
• Medication or treatment side effects. (For example, high MCV may be a side effect of chemotherapy.)

If the results are abnormal, what are the next steps?

The next steps depend on what’s causing your abnormal MCH levels. For example, you may need tests to check your iron stores if your provider suspects an iron deficiency is causing low MCH levels. You may need other tests if your test results point to a separate condition.

Your healthcare provider can advise you based on your results.