MCV, MCH, MCHC and RDW
These are measurements or calculations related to red blood cells (RBCs) and are components of the full blood count (FBC), a commonly requested test used for a variety of purposes.
- Mean corpuscular volume (MCV) is a measurement of the average size of your RBCs. The MCV is elevated when your RBCs are larger than normal (macrocytic), for example in anaemia caused by vitamin B12 deficiency. When the MCV is decreased, your RBCs are smaller than normal (microcytic) as is seen in iron deficiency anaemia or thalassaemias.
- Mean corpuscular haemoglobin (MCH) is a calculation of the average amount of oxygen-carrying haemoglobin inside a red blood cell. Macrocytic RBCs are large so tend to have a higher MCH, while microcytic red cells would have a lower value.
- Mean corpuscular haemoglobin concentration (MCHC) is a calculation of the average concentration of haemoglobin inside a red cell. Decreased MCHC values (hypochromia) are seen in conditions where the haemoglobin is abnormally diluted inside the red cells, such as in iron deficiency anaemia and in thalassaemia. Increased MCHC values (hyperchromia) are seen in conditions where the haemoglobin is abnormally concentrated inside the red cells, such as in burn patients and hereditary spherocytosis, a relatively rare congenital disorder.
- Red cell distribution width (RDW) is a calculation of the variation in the size of your RBCs. In some anaemias, such as pernicious anaemia (due to vitamin B12 deficiency), the amount of variation (anisocytosis) in RBC size (along with variation in shape - poikilocytosis) causes an increase in the RDW.