Red blood cell distribution width is a test which is part of the complete blood count and measures the variation in red blood cell size. Normal red blood cells are similar in size but variations can be indicative of some causes of anaemia.
Red blood cells are the most common type of blood cell in circulation. Their main function is to distribute oxygen around the body via the protein, haemoglobin.
Red blood cells have no nucleus which means they have a greater surface area and this enhances their ability to transport oxygen. They are a biconcave disc shape with a depressed centre. The normal size of a red blood cell is between 6 and 8 µm (micrometres) and they have a thickness of 2 µm.
Under some physiological conditions, red blood cells may undergo an increase or decrease in size. The makeup of the cell allows these changes to take place. Usually, an RBC distribution width which is lower than the conventional parameters is deemed clinically meaningless. However, an increase above the normal can indicate that an individual’s red blood cells are not equally sized (anisocytosis).
The condition where red blood cells are not equal in size is called anisocytosis. There are some physiological conditions which can cause red blood cells to be different sizes, including:
Several disorders can result in anisocytosis, including:
RBC distribution width can help to give a good indication of the health status of individuals. It is often used in conjunction with mean corpuscular volume, the average size of red blood cells, to diagnose different anaemias. Anaemias can be classified according to the size of the cell i.e.:
Your diet can help to keep anaemia at bay. Eating a healthy and balanced diet and ensuring you get all the nutrients you need.
Red blood cells need iron to function efficiently. Good sources of dietary iron include:
Plant-based sources of iron such as dark green leafy vegetables, nuts, seed, pulses and fortified cereals may be absorbed better in the presence of vitamin C. Try eating fortified breakfast cereals alongside a glass of orange juice or swap chips for a jacket potato with a side of green leafy veg – be sure to eat the skin of the potato. You should also refrain from drinking tea with your meals as this can affect iron absorption. Instead, you should drink it between meals to ensure you absorb iron effectively.
You also need to make sure your vitamin B12 levels are adequate too. However, you should avoid eating too much as this can have adverse effects and could contribute to a high mean corpuscular volume (MCV). There is a strong association between MCV and RBC distribution width. Early vitamin B12 deficiency can present with a normal MCV but increased distribution width, however, increased MCV and width can cause full blown deficiency.
Good sources of vitamin B12 include:
As vitamin B12 is found only in animal products, vegetarians and vegans can find themselves at risk of becoming deficient. Therefore, these groups may need to consider supplementation.
Exercise is an important aspect of a healthy lifestyle. Regular exercise can help to increase blood flow to muscles which enables oxygen to reach the tissues. Exercise also helps to increase the oxygen carrying capacity of red blood cells.
Both too much and too little iron can influence energy levels and could affect your ability to exercise. Low iron can also influence how well and quickly your muscles repair themselves after exercise. Iron deficiency anaemia may also be more common in athletic groups and may need iron supplementation.
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 British Dietetic Association. (2017). Food Fact Sheet: Iron. Available at: https://www.bda.uk.com/foodfacts/iron_food_fact_sheet.pdf
 Lane, D, J, R and Richardson, D, R. (2014). The Active Role of Vitamin C in Mammalian Iron Metabolism: Much More than Just Enhanced Iron Absorption. Free Radical Biology and Medicine: 75, pp 69-83.
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