MCH blood test: normal range and what the result means

MCH (Mean Corpuscular Hemoglobin) is one of the red blood cell indices, and it is calculated together with the complete blood count (CBC). It shows the average amount of haemoglobin in a single red blood cell, measured in picograms (pg). Haemoglobin is the protein in red blood cells that carries oxygen from the lungs to the tissues, so MCH indirectly reflects how well each cell can do that job. MCH is closely related to another red blood cell index, MCV (the mean corpuscular volume): when the red blood cells are smaller and contain less haemoglobin (microcytic, hypochromic anaemia), MCH tends to be low; when the red blood cells are larger (macrocytic anaemia), MCH is often raised. That is why MCH on its own is rarely assessed in isolation — the laboratory and the doctor look at it together with MCV, MCHC, haemoglobin and haematocrit values, so that the type of anaemia and its possible cause can be told apart.

• When a complete blood count (CBC) is done as a preventive check or because of other complaints — MCH is always included in the red blood cell indices
• When you feel tired, weak, short of breath or have other signs of anaemia
• When there are disturbed eating habits, heavy blood loss or chronic illnesses that can affect blood formation
• When blood counts are being monitored during treatment (for example chemotherapy, or taking iron or vitamin B12 preparations)
• When a change in MCV was noticed in an earlier complete blood count — MCH helps to pin down the type of anaemia

How to prepare

• No special preparation is needed for the MCH test (as part of the complete blood count)
• If other blood tests are taken at the same time, the doctor may ask you not to eat or drink for a few hours

Reference range

According to MedlinePlus, the MCH range for adults is 27-32 pg. The exact limit may differ slightly depending on the laboratory analyser — you will find the exact interval on your own result sheet.

A raised MCH

A raised MCH is most often seen together with a raised MCV — when the red blood cells are larger than usual (macrocytic anaemia). The most common causes are a vitamin B12 or folic acid deficiency, and also liver disease. To establish the exact cause, all the red blood cell indices have to be assessed together.

• Vitamin B12 deficiency (pernicious anaemia)
• Folic acid (vitamin B9) deficiency
• Liver disease
• Some bone marrow disorders

What to discuss with a doctor when MCH is raised

• Assessing MCV, MCHC, haemoglobin and haematocrit together — whether the overall picture of macrocytic anaemia is there
• Vitamin B12 and folic acid in the blood
• Liver markers (ALT, AST, GGT)
• Discussing the symptoms and eating habits with the doctor

A low MCH

A low MCH is most often seen together with a low MCV — when the red blood cells are smaller and contain less haemoglobin (microcytic, hypochromic anaemia). The most common cause is iron deficiency, less often inherited haemoglobin disorders such as thalassaemia.

Causes of a low MCH

• Iron deficiency anaemia — the most common cause
• Thalassaemia — an inherited type of haemoglobin disorder

What to discuss with a doctor when MCH is low

• Assessing MCV, haemoglobin, haematocrit and ferritin together — to check the iron stores
• A possible cause of blood loss
• Family history, if thalassaemia is suspected
• Discussing with the doctor whether additional iron markers are needed