MCH blood test: normal range explained

MCH measures the average mass of haemoglobin in one red blood cell, in picograms. It is one of the red cell indices that a CBC reports beside MCV (cell size) and MCHC (haemoglobin concentration), and Lab Tests Online UK lists RDW with them.

Because haemoglobin is what carries oxygen, MCH shows whether each cell is carrying its usual load. Cells with less haemoglobin than usual are called hypochromic, and MedlinePlus says this is most often due to low iron.

Doctors read MCH with the other indices to help find the cause and type of anaemia, when there are too few red blood cells or too little haemoglobin. Testing.com lists feeling weak or tired more often than usual, and later shortness of breath, among the symptoms that prompt a CBC.

MCH arrives with every CBC, so it is also seen at routine check-ups and when a CBC is ordered for another reason. MedlinePlus says a CBC helps monitor conditions such as anaemia, infections and blood disorders.

MCH follows the size of the red cells and the haemoglobin in them, so the same things move it.

• Iron deficiency and thalassaemia lower MCH, because the cells are smaller and hold less haemoglobin.
• Low folate or vitamin B12 and chemotherapy raise MCH, because the cells are larger.
• Sudden blood loss, long-term disease or kidney failure can cause anaemia with a normal MCH.
• Diet, activity level, medicines, a menstrual period and not drinking enough water can affect CBC results.
• Each laboratory sets its own reference range from its equipment and the people it serves.