Haematocrit (HCT)

What Is Haematocrit?

Haematocrit is the measurement of how much of the total volume of blood is made up of red blood cells. It is usually measured as part of a full blood count and forms part of the diagnoses of anaemia.

Which tests include this marker?

What Role Does It Play in The Body?

Red blood cells are the most abundant cell in the blood.

A haematocrit test measures the amount of space in the blood which is occupied by red blood cells.

How Does Haematocrit Affect My Wellbeing?

A low haematocrit can indicate anaemia. Anaemia can cause a range of side effects, including:

  • Lack of energy
  • Feeling tired all the time
  • Shortness of breath
  • Feeling dizzy
  • Nauseous
  • Skin may be paler than usual
  • Difficulty sleeping
  • Difficulty concentrating

Some of the causes of anaemia can include:

  • Poor nutrition – lack of iron, vitamin B12 etc
  • Bleeding
  • Kidney disease
  • Inflammatory diseases
  • Liver cirrhosis
  • Some medication can cause anaemia

An increased haematocrit, however, can be a sign of dehydration. With an adequate intake of fluid, the levels should return to normal. However, it may also be a result of a bone marrow issue such as polycythaemia. Polycythaemia Vera can lead to an increased production of red blood cells and is caused by a mutation in a gene which regulates the production of red blood cells.[2] Apparent polycythaemia, on the other hand, is caused by a reduction in plasma volume – the liquid part of the blood. This can be related to lifestyle factors such as a high body mass index, increased alcohol consumption, smoking and the use of medication such as diuretics.[3] Some people can experience symptoms such as:

  • Headaches
  • Fatigue
  • Dizziness
  • Blurred vision
  • Itchy skin
  • Stomach pain
  • Flushed skin[4]

How Can I Improve My Result?

A nutrient which is essential for red blood cell health is iron. But a healthy diet is not the only lifestyle factor which can help to keep our haematocrit within normal parameters. Factors such as alcohol intake, smoking, weight gain and exercise should all be considered to help ensure good health.


A good source of iron is red meat, and this should be eaten at least once per week. In women who are menstruating, their iron intake may need to be increased around the time of menstruation. However, those who follow a vegetarian diet should get their iron sources from elsewhere, which can be difficult, but sources include:

  • Fortified cereals
  • Green leafy vegetables e.g. spinach
  • Dried fruit
  • Pulses
  • Nuts
  • Seeds

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.[5] 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.[6]

Try to keep your weekly alcohol limit within the guidelines of 14 units per week. You should also ensure that you keep yourself adequately hydrated – you don’t just have to drink water, tea, coffee, fruit juice and squash all count but be aware of their sugar contents.


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.[7] Iron deficiency anaemia may also be more common in athletic groups and may need iron supplementation.11

You should try to complete around 150 minutes of aerobic exercise per week. Activities could include walking, jogging, swimming or cycling but you should complete your minutes over a period of a few days and not all at once.

Tests that include this marker

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[1] Quintó, L., Aponte, J, J., and Menéndez, C et al., (2006). Relationship Between Haemoglobin and Haematocrit in the Definition of Anaemia. Tropical Medicine and International Health: 11(8).

[2] McMullin, M, F., Wilkins, B, S and Harrison, C, N. (2015). Management of Polycythaemia Vera: A Critical Review of Current Data. British Journal of Haematology: 172(3).

[3] Oxford University Hospitals. (2011).  Diagnosis in Primary Care and Referral Pathway for Patients with a Raised Haematocrit. Available at: http://nssg.oxford-haematology.org.uk/general-haematology/files/raised-haematocrit.pdf

[4] National Health Service. (2016). Polycythaemia. Available at: https://www.nhs.uk/conditions/polycythaemia/

[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.

[7] Beard, J and Tobin, B. (2000). Iron Status and Exercise. The American Journal of Clinical Nutrition: 72(2), pp 594S-597S.

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