Mean corpuscular volume (MCV) measures the average size of red blood cells in the body. MCV is a useful marker for the diagnosis of anaemia. It is often used as part of a full blood count along with other red cell indices.
The mean corpuscular volume is a useful assessment tool for diagnosing anaemia. It is often used in conjunction with other red cell measurements such as mean cell haemoglobin and mean cell haemoglobin concentration. These measurements reflect the volume, size and haemoglobin content of red blood cells.
The main function of red blood cells, also known as erythrocytes, is to transport the gases, oxygen and carbon dioxide, from the lungs to the tissues and vice versa. Removing carbon dioxide from the body also helps to maintain the pH of the blood.
Up to 3 million red blood cells are produced in the bone marrow every second and released into circulation. They are the most abundant blood cell, but they are small at about 6 micrometres in diameter. Red blood cells have a lifespan of approximately 120 days, at which point they are removed from circulation by special cells called macrophages in the liver and spleen.
Unlike most cells, red blood cells do not contain a nucleus and are biconcave in shape which means they have a bigger surface area, giving them more room to store haemoglobin. Haemoglobin is a vital protein in the human body and has an important function. The main role of haemoglobin is to transport oxygen from the lungs to all cells and tissues in the body. Approximately 96% of the dry weight of red blood cells is haemoglobin. The structure of haemoglobin consists of four heme molecules each of which contains an iron ion. Each of the iron ions can bind to one molecule of oxygen forming oxyhaemoglobin. When oxyhaemoglobin reaches a cell which requires oxygen, the oxygen dissociates from the haemoglobin and enters the cell.
An increased mean corpuscular volume is an indicator of macrocytic anaemia where red blood cells are larger than normal. The condition is relatively common and is often caused by a nutrient deficiency, particularly vitamin B12 or folate. Vitamin B12 deficiency is often caused by an inadequate dietary intake of the vitamin. Individuals who are most at risk of vitamin B12 deficiency are those who follow a vegan diet, particularly because much of our vitamin B12 comes from animal-based sources. Alcoholism can also cause an elevated MCV.
A reduced MCV can indicate microcytic anaemia with a common cause being iron deficiency. Again, this is usually caused by a lack of dietary intake of iron.
Microcytic anaemia is where red blood cells are smaller than usual and are characterised by a low MCV. The most common cause of this type of anaemia is iron deficiency. The causes of iron deficiency anaemia vary but it can be caused by blood loss or reduced absorption of iron. In females who are of menstruating age, the most common cause is menstrual blood loss and the most common cause in men and non-menstruating women is gastrointestinal blood loss.
Macrocytic anaemia results in an elevated MCV OF >100fL. Macrocytic anaemia can be split into two groups, megaloblastic and non-megaloblastic. Megaloblastic anaemia is where the bone marrow produces unusually large, immature red blood cells. The most common cause of this type of anaemia is vitamin B12 deficiency. It is usually caused by malnutrition in groups such as vegans or vegetarians or can be due to malabsorption.
The symptoms of most types of anaemia are relatively similar and include:
Vitamin B12 deficiency can cause many symptoms and the severity of the condition can worsen over time, especially if it is left untreated. The symptoms of vitamin B12 deficiency can include the normal symptoms of anaemia as well as:
A nutrient which is essential for red blood cell health is iron. Good sources of iron are red meat and liver. It is recommended that red meat is consumed once per week to help keep iron levels within normal parameters. Women who are of menstruating age need to keep their iron intake increased, particularly around the time of their periods. Individuals who follow a vegan or vegetarian diet will need to get their iron from plant-based sources.
Good food sources of iron are:
The absorption of iron from plant-based sources is better when vitamin C is present. For example, fortified breakfast cereals paired with a glass of orange juice. Tea can affect the absorption of iron, so you should refrain from drinking tea with your meals and switch to drinking it between meals instead. 
Iron levels can be influenced by too much or too little exercise. Not having enough iron can affect your muscles ability to recover following exercise.
A high mean corpuscular volume level can be caused by macrocytic anaemia, a major cause of which is vitamin B12 deficiency. Therefore, it is important to ensure you are getting enough vitamin B12 in your diet. People who find it more difficult to get a good amount of B12 in their diet are those who follow a vegan diet. The reason for this is because much of the vitamin B12 comes from animal products. Vegans and possibly vegetarians may need to supplement their diet.
Good sources of vitamin B12 are:
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