July 21, 2020

What is Haemoglobin?

Haemoglobin is a protein present in red blood cells, responsible for transporting oxygen from the lungs to cells in the body. Haemoglobin gives red blood cells their distinctive colour. Haemoglobin levels differ between individuals, but men usually have higher haemoglobin levels than women.[1]

Why take a Haemoglobin blood test?

A haemoglobin blood test measures the amount of haemoglobin present in your blood. The haemoglobin concentration gives a good insight into the blood’s ability to carry oxygen around the body.

Because haemoglobin carries oxygen from the lungs to cells around the body, low levels can signify anaemia where your body isn’t getting enough oxygen. Anaemia can cause symptoms like weakness and fatigue. Whereas, a high level can be a sign of polycythaemia where there are too many red blood cells in circulation.[2]

You should make sure you are adequately hydrated when testing your haemoglobin levels. If you’re not, it can cause an abnormally high result.

You can check your level of haemoglobin together with other red blood cells within Forth’s Vitality and Ultimate blood tests.

What function does Haemoglobin have in the body?

The main function of haemoglobin in the body is to transport oxygen from the lungs to all the cells and tissues in the body. The protein makes up approximately 96% of the dry weight of red blood cells. Haemoglobin is made up of four heme molecules each of which contains an iron ion. Each iron ion can bind with one molecule of oxygen. When oxygen is bound to haemoglobin, it is known as oxyhaemoglobin. Once oxyhaemoglobin reaches a cell in need of oxygen, the oxygen dissociates from the haemoglobin enters the cell. [3]

Another role of haemoglobin is to transport carbon dioxide from the tissues to the lungs. Carbon dioxide is a waste product of respiration, 80% of which is transported via plasma. Carbon dioxide doesn’t compete with oxygen for its binding site in haemoglobin, instead, it attaches to the protein structure.

Haemoglobin also helps to maintain the pH of the blood at 7.4. If carbon dioxide builds up in the blood, then the pH lowers but this can be changed through breathing or ventilation.

How do changes in Haemoglobin affect health and wellbeing?

High levels of haemoglobin can indicate dehydration. Dehydration can make you feel unwell and has some unpleasant symptoms.

A low haemoglobin concentration can be a sign of anaemia, particularly iron deficiency. Anaemia occurs when the body doesn’t have enough red blood cells to meet its needs. As a result, it can cause a variety of unpleasant symptoms which can affect your everyday life.

What can cause Haemoglobin to change?

The normal haemoglobin values are between 120 and 180 g/L of blood, but this can vary according to gender, age and ethnicity. An increased haemoglobin count can be caused by:

  • Dehydration
  • Severe lung disease
  • Excess production of red blood cells in the bone marrow called polycythaemia

A reduced haemoglobin level may be caused by:

  • Iron deficiency
  • Vitamin deficiencies
  • Kidney disease
  • Bleeding
  • Inflammatory disorders
  • Liver cirrhosis
  • Haemolysis
  • Bone marrow failure
  • Bone marrow cancer
  • Infection


What are the most common symptoms?

The common symptoms of dehydration are:

  • Thirst
  • Dry mouth, lips and eyes
  • Feeling dizzy or lightheaded
  • Fatigue or feeling tired
  • Headaches
  • Dark yellow and strong-smelling pee
  • Peeing less often usually less than four times per day[4]

Anaemia may or may not present with any symptoms. If the condition has developed slowly, over time you may not feel any different or notice any symptoms. However, it is likely you will eventually start to notice some symptoms, including:

  • 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 Haemoglobin in the healthy range

A nutrient which is essential for red blood cell health is iron. A good source of iron is 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. [5] 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. [6]

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.

Dehydration is the most common cause of an increased haematocrit level. This is because blood plasma volume is reduced, as water is distributed around the body to the cells and tissues which need it most. You should aim to drink little and often throughout the day. Thirst is an early sign of dehydration, so you should try to avoid getting thirsty. You may need to drink more if you are exposed to increased temperatures, are exercising or experiencing diarrhoea and vomiting.

- Health scores calculated



[1] World Health Organisation. (2014). Annex 1 Haemoglobin and Iron: Information for Blood Donors. In: Blood Donor Counselling: Implementation Guidelines.

[2] Lab Tests Online UK. (2016). Haemoglobin.

[3] Panawala, L. (2017). What is the Function of Hemoglobin in the Human Body. Pedia. Available at: https://www.researchgate.net/publication/313841668_What_is_the_Function_of_Hemoglobin_in_the_Human_Body

[4] NHS. (2017). Dehydration. Available at: https://www.nhs.uk/conditions/dehydration/

[5] 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.

[6] 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.

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This information has been medically reviewed by Dr Nicky 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.

Dr Nicky Keay

Dr Nicky Keay

BA, MA (Cantab), MB, BChir, MRCP.