Mean corpuscular haemoglobin (MCH) is the average amount of haemoglobin per red blood cell in a blood sample. MCH is used to help diagnose the type, cause, and severity of anaemia. You will see the MCH reported as part of a Full Blood Count (FBC) test.
The normal range for MCH 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 haemoglobin and smaller red blood cells usually have less haemoglobin simply due to their size.
A low MCH is known as hypochromic, because there is less haemoglobin in the red cells, which give them their red colour. In this case, the red blood cells appear paler. A high MCH with anaemia is known as hyperchromic anaemia.
You can still be anaemic and have a normal MCH though. This may occur with sudden blood loss, chronic illnesses, and blood infections and in kidney failure.
High MCH levels may indicate the presence of a macrocytic anaemia and can have a variety of causes, including liver disease, and deficiencies of vitamin B12 and folic acid.
When your MCH is low, you may have iron-deficiency anaemia. This type of anaemia 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.