MCHC (mean corpuscular haemoglobin concentration)

MCHC is one of the red-cell indices reported with a full blood count, calculated from the haemoglobin and the proportion of blood made up of red cells (the haematocrit). It describes the average concentration of haemoglobin within a red cell — essentially how densely the oxygen-carrying pigment is packed, and therefore how deeply coloured the cell is. Unlike MCH, which is the amount of haemoglobin per cell, MCHC is the amount relative to cell volume, so it is less affected by cell size. Its main value is in helping classify anaemia. A low MCHC means the red cells are pale (hypochromic), the classic pattern of iron deficiency and of some other conditions where haemoglobin production is impaired, such as thalassaemia. A high MCHC is less common and more specific: it points chiefly to hereditary spherocytosis, an inherited condition where red cells are small and dense, and can also appear as an artefact (for example from cold agglutinins or a lipaemic sample). MCHC is read together with MCV, MCH and the red-cell distribution width to build a picture of the size and colour of the cells.

• Hereditary spherocytosis — the classic cause; small, dense, over-concentrated red cells.
• Severe or long-standing dehydration — can nudge it up.
• Autoimmune haemolysis (cold agglutinins) — often a laboratory artefact rather than a true rise.
• A lipaemic or abnormal sample — a spuriously high reading that the lab will flag.

• Iron deficiency — the commonest cause; pale (hypochromic) red cells.
• Thalassaemia and other disorders of haemoglobin production.
• Anaemia of chronic disease — sometimes mildly low.