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Red Blood Cell (RBC)

What are red blood cells?

Red blood cells are a major constituent of the blood and every second up to 3 million red blood cells are made by the bone marrow and released into circulation. They are the most common blood cell and they have a lifespan of approximately 120 days. Once they are old or damaged, they are removed from circulation by special cells in the spleen and liver.[1]

Red blood cells contain a protein called haemoglobin which gives them their distinctive red colour. Haemoglobin is responsible for transporting oxygen around the body to cells which require it, it also removes the waste product, carbon dioxide from circulation.[1]

Why take a red blood cell blood test?

There are certain tests which give an insight into the health of red blood cells. Red cell indices including mean cell volume, mean cell haemoglobin, mean cell haemoglobin concentration and red cell distribution width give measurements relating to the volume, size and the amount of haemoglobin present in red blood cells. These measurements can help to diagnose or monitor conditions which affect the size and shape of red blood cells.[2]

A red blood cell count, on the other hand, tells us how many red blood cells are in a litre of blood. High or low red blood cell counts can be indicative of disease.[3]

You can check your level of red blood cells within Forth’s Vitality and Ultimate blood tests. For those who lead active lifestyles Forth also offers a home finger-prick blood test called Baseline plus which includes both red blood cell count as well as 16 other biomarkers.

What function do red blood cells have in the body?

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.[4]

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.[5]

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.[6]

How do changes in red blood cells affect health and wellbeing?

A dysfunction in red blood cells can signify anaemia, kidney disease, bone marrow failure, malnutrition or bleeding. Plus, it may also indicate a nutritional deficiency.  The symptoms of these illnesses can affect our wellbeing and negatively impact our quality of life.

A high red blood cell count can indicate several diseases, including:

  • congenital heart disease
  • obstructive lung disease
  • overproduction by bone marrow
  • dehydration

If you are worried about your RBC level or just want to check where you fall on the range, you can test your level with a simple at-home blood test.

What can cause red blood cells to change?

Nutritional deficiencies like vitamin B12 and folate can lead to a low red blood cell count. Vitamin B12 is an essential vitamin needed to produce DNA and cell metabolism. Therefore, the consequences of vitamin B12 deficiency can be severe. Humans are unable to make their own vitamin B12 and so dietary intakes are important. Vegetarians and vegans, as well as the elderly population, are most at risk of deficiency, particularly because the majority of vitamin B12 comes from animal sources. Deficiency is multifactorial and is caused by an insufficient intake or an acquired or inherited defect which interrupts B12 absorption. We have a relatively high storage of vitamin B12 and so it can take years to deplete these stores and become deficient.[7]

Although some of the causes of vitamin B12 deficiency can’t be prevented, if it is caused by poor diet or malnutrition it is possible to reduce the risk. [8]

Folate deficiency is another nutritional deficiency which causes a low red blood cell count. The symptoms are like vitamin B12 deficiency and just like the vitamin, our folate levels are reliant on our dietary intake. Folate is especially important during pregnancy and is required for adequate foetal and placental development. [9] All females are advised to supplement their intake with 400 micrograms of folic acid while they try to get pregnant and then for the first 12 weeks of pregnancy. Folic acid reduces the risk of neural tube defects such as spina bifida. [10]

What are the most common symptoms?

The symptoms of vitamin B12 and folate deficiencies develop gradually over time and include:

  • A sore, red tongue called (glossitis)
  • Pins and needles
  • Disturbed vision
  • Feeling irritable
  • Depression
  • Mouth ulcers
  • A pale-yellow tinge to your skin
  • A decline in mental function

The symptoms of most types of anaemia are similar and include:

  •  Pale skin
  • Feeling tired and weak most of the time
  • Dizziness
  • Not able to complete as much exercise as you usually would
  • Feeling like you are short of breath after exercise
  • Experience heart palpitations[5]

How to keep red blood cells in the healthy range

The components of blood including red blood cells are detrimental to the health of the human body. The transportation of oxygen around the body via haemoglobin is vital for the metabolic processes required to sustain life. Our lifestyle can greatly impact the health of red blood cells. For example, chronic obstructive pulmonary disorder (COPD) is associated with a high red cell count. [11] The disease is treatable and preventable and is caused by an abnormal inflammatory response by the lungs to toxic particles or gases, such as those found in cigarette smoke. Therefore, by not smoking or giving up the risk of COPD is reduced.

Diet is also an important factor in the health and function of red blood cells. 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:

  • red meat
  • liver
  • green leafy vegetables e.g. spinach
  • dried fruit
  • pulses
  • nuts
  • seeds

The absorption of iron from plant-based sources is better when vitamin C is present.[12] 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. [13]

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.

Vitamin B12 deficiency is associated with a low red cell count.  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:

  • meat
  • fish like salmon or cod
  • eggs
  • milk and dairy products
  • vegan-friendly products
    • yeast extracts like marmite
    • fortified breakfast cereals[14]

Exercise is fundamental for our overall health, too. Regular exercise helps to increase blood flow to muscles, enabling oxygen to reach the tissues which require it. During exercise, there is an increased demand for oxygen which is met by increasing muscle blood flow. Physical training increases the mass of haemoglobin which increases the amount of oxygen which can be carried by red blood cells. [15]

Red Blood Cell (RBC) Tests

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[1] Dean L. (2005). Blood Groups and Red Cell Antigens [Internet]. Bethesda (MD): National Center for Biotechnology Information (US). Chapter 1, Blood and the cells it contains. Available from:

[2] Lab Tests Online UK. (2015). Red Cell Indices. Available at:

[3] Lab Tests Online UK. (2012). Red Blood Cell Count. Available at:

[4] Kuhn, V et al. (2017). Red Blood Cell Function and Dysfunction: Redox Regulation, Nitric Oxide Metabolism, Anemia. Antioxidants and Redox Signaling: 26(13).

[5] Dean L. Blood Groups and Red Cell Antigens [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2005. Chapter 1, Blood and the cells it contains. Available from:

[6] Panawala, L. (2017). What is the Function of Hemoglobin in the Human Body? Pedia. Available at:

[7] Hannibal, L et al. (2016). Biomarkers and Algorithms for the Diagnosis of Vitamin B12 Deficiency. Front Mol Biosci.

[8] Hunt, A., Harrington. D and Robinson, S. (2014). Vitamin B12 Deficiency. BMJ: 349.

[9] Castaño, E., Piñuñuri, R., Hirsch, S and Ronco, A, M. (2016). Folate and Pregnancy, Current Concepts. It is Required Folic Acid Supplementation? Rev Chil Pediatr: 88(2), pp 199-206.

[10] NHS Choices. (2018). Why Do I Need Folic Acid in Pregnancy? Available at:

[11] Littner, M, R. (2011). In the Clinic: Chronic Obstructive Pulmonary Disease. Annals of Internal Medicine. Available at:

[12] 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.

[13] Zijp, I, M., Korver, O and Tijburg, L, B, M. (2000). Effect of Tea and Other Dietary Factors on Iron Absorption. Critical Reviews in Food Science and Nutrition: 40(5), pp 371-398.

[14] NHS. (2019). Treatment Vitamin B12 or Folate Deficiency Anaemia. Available at:

[15] Mairbäurl, H. (2013). Red Blood cells in Sports: Effects of Exercise and Training on Oxygen Supply by Red Blood Cells. Frontiers in Physiology: 4.

Medically reviewed

This information has been medically reviewed by Dr Nicola Keay.

Nicola has extensive clinical and research experience in the fields of endocrinology and sport and exercise medicine. Nicky is a member of the Royal College of Physicians, Honorary Fellow in the Department of Sport and Exercise Sciences at Durham University and former Research Fellow at St. Thomas’ Hospital.

Nicky Keay
Dr Nicola Keay

BA, MA (Cantab), MB, BChir, MRCP.​

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