Haematocrit (HCT)

July 21, 2020

What is Haematocrit?

Haematocrit, also known as packed cell volume (PCV), is the measurement of the proportion of blood which is made up of cells. It is usually presented as a percentage or fraction of cells in the blood. For example, a haematocrit or PCV of 50% means there are 50 millilitres of cells per 100 millilitres of blood.[1]

Haematocrit is usually tested as part of a full blood count and can be used for a variety of reasons.

Why take a Haematocrit blood test?

A haematocrit blood test can help to identify a variety of illnesses and conditions. It can be used to monitor treatment for anaemia or dehydration.

A normal haematocrit for men is between 40 and 54% while for women it is between 36 and 48%. The test is based upon plasma volume and so, dehydration can affect the overall result. Many anaemias can be diagnosed with a haematocrit and haemoglobin reading.[2]

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

What function does Haematocrit have in the body?

Red blood cells are the most abundant blood cell in the human body. The purpose of haematocrit is to measure the amount of space in the blood which is occupied by red blood cells.

The main function of red blood cells is to transport oxygen and carbon dioxide from the lungs to the tissues and to maintain the equilibrium of the body’s acid-base levels.[3] Red blood cells have an iron-containing protein called haemoglobin within them which is responsible for carrying oxygen around the body. Haemoglobin gives red blood cells their distinctive colour. If red blood cells levels fall, this may indicate the presence of anaemia and will result in a low haematocrit count. Equally, an increased haematocrit may signal that too many red blood cells are being produced and are causing a condition called polycythaemia.[4]

How do changes in Haematocrit affect health and wellbeing?

The haematocrit percentage indicates the amount of space within the blood that is occupied by red blood cells. Therefore, a low haematocrit suggests there are too few red blood cells being produced, while an increased haematocrit reading indicates there are too many red blood cells in circulation. Because the haemoglobin in red blood cells has an important function in transporting gases to and from the body, a fluctuation in red blood cell levels can affect our health.

For example, a low haematocrit usually signals an individual has anaemia, a condition where your body doesn’t have enough red blood cells or haemoglobin to meet the needs of the body.

Equally, polycythaemia occurs when the bone marrow overproduces red blood cells of its own accord.

What can cause Haematocrit to change?

The most common cause of increased haematocrit is dehydration.

The causes of anaemia can be varied, but it’s generally because of one three reasons:

  1. The body isn’t making enough red blood cells possibly due to a nutrient deficiency like iron, vitamin B12 or folate.
  2. Red blood cells are being broken down too quickly. This is called haemolytic anaemia.
  3. Significant blood loss has occurred possibly because of trauma or gradual blood loss over a prolonged period. A good example of this is the female menstrual cycle, women who have heavy periods are at risk of anaemia due to blood loss. Individuals with peptic ulcers or haemorrhoids are also at risk.[5]

Other causes of a reduced haematocrit are:

  • Inflammatory conditions
  • Bleeding
  • Kidney disease
  • Liver cirrhosis
  • Bone marrow disorders
  • Some medications, particularly chemotherapy

The most common cause of increased haematocrit is dehydration.

Polycythaemia is caused by the bone marrow producing more red blood cells than the body needs of its own accord. However, it is often caused by factors outside the bone marrow. This is called secondary polycythaemia and is caused by:

  • Excessive alcohol drinking
  • Some lung or heart diseases
  • Smoking
  • Liver or kidney disease
  • Some tumours
  • Rare inherited haemoglobins.


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[6]

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]

Polycythaemia, on the other hand, can cause symptoms such as:

  • Headaches
  • Blurred vision
  • Confusion
  • Dizziness
  • Tiredness
  • Red skin
  • Tummy discomfort
  • Bleeding issues like nosebleeds and bruising
  • Gout
  • Itchy skin[7]

How to keep Haematocrit 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. [8] 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. [9]

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] Lab Tests Online UK. (2012). PCV. Available at: https://labtestsonline.org.uk/tests/pcv

[2] Billett, H, H. (1990). Chapter 151 Hemoglobin and Hematocrit. In: Clinical Methods: The History, Physical and Laboratory Examinations.

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

[4] Lab Tests Online. (2015). Hemoglobin. Available at: https://labtestsonline.org/tests/hemoglobin

[5] Mahendra, P. (2019). Anaemia. Available at: https://www.bupa.co.uk/health-information/heart-blood-circulation/anaemia

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

[7] NHS. (2019). Polycythaemia. Available at: https://www.nhs.uk/conditions/polycythaemia/

[8] 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.

[9] 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.