Haematocrit%
Red-cell concentration
Also known as: Hematocrit, HCT
Typical optimal range
40–52 %
Female
A typical optimal range is broadly 40–52%, though reference intervals differ between laboratories and between men and women, so your result should always be interpreted against your own lab's figures. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Interpretation of full blood count results, including haematocrit, follows NHS and laboratory medicine guidance; NICE guideline NG24 covers the recognition and management of anaemia in chronic kidney disease, and NICE guidance on anaemia (including iron-deficiency anaemia) provides further clinical context.
What is Haematocrit?
Haematocrit (HCT) is the percentage of your total blood volume that is made up of red blood cells. It is measured as part of a full blood count (FBC), one of the most routinely requested blood tests in UK clinical practice. Because red blood cells carry oxygen to every tissue in the body, haematocrit gives a quick, reliable snapshot of whether your blood has the capacity to do that job effectively. It closely mirrors haemoglobin and together they help clinicians identify conditions ranging from anaemia to disorders of excess red cell production.
What a high Haematocrit means
A raised haematocrit means red blood cells are taking up a larger share of your blood volume than expected, which can make the blood thicker and harder for the heart to pump. This is a prompt to look more closely rather than a diagnosis in itself.
- Dehydration. When you are not drinking enough fluid, plasma volume falls while the red cell mass stays the same, so the percentage of red cells appears higher. This is one of the most common and easily reversible causes of a mildly elevated haematocrit.
- Polycythaemia. Polycythaemia vera is a bone marrow condition in which the body produces too many red blood cells. Secondary polycythaemia can arise from chronic low oxygen levels, such as in untreated sleep apnoea or chronic lung disease, prompting the body to compensate by making more red cells.
- Testosterone therapy or EPO use. Exogenous testosterone and erythropoietin (EPO) both directly stimulate red blood cell production. Haematocrit monitoring is a standard part of clinical oversight for patients on testosterone replacement therapy in the UK.
A single mildly elevated reading, particularly after illness, heavy exercise, or in warm weather, may simply reflect dehydration. Repeat testing after rehydrating is often informative before further investigation is pursued.
What a low Haematocrit means
A below-range haematocrit is the classic laboratory fingerprint of anaemia — meaning there are too few red blood cells, or they are smaller or less haemoglobin-rich than normal — and warrants further investigation to find the underlying cause.
- Iron-deficiency anaemia. Iron deficiency is the most common cause of a low haematocrit in the UK, particularly in women of reproductive age. Insufficient dietary iron, heavy periods, or poor absorption all reduce the body's ability to build healthy red blood cells.
- Other nutritional or chronic causes. Deficiencies in vitamin B12 or folate produce a different pattern of anaemia with larger, fewer red blood cells. Chronic kidney disease, inflammatory conditions, and certain medications can also suppress red cell production and lower haematocrit over time.
A low haematocrit is almost always worth discussing with your GP, who will usually request further tests — such as ferritin, B12, folate, and a blood film — to identify the specific type of anaemia before any treatment is started.
Should I be worried?
A single haematocrit result outside the reference range is a useful signal, not a verdict. Mild deviations are common and often explained by straightforward factors like hydration status or the timing of the test. That said, a persistently low or high haematocrit — especially one that is trending in the wrong direction or is accompanied by symptoms such as fatigue, breathlessness, dizziness, or headaches — is worth discussing with your GP. They will usually look at haematocrit alongside haemoglobin, mean cell volume (MCV), ferritin, and other full blood count components to build a complete picture, and can refer you for specialist assessment if a condition like polycythaemia vera or significant anaemia needs to be ruled out.
What actually helps
Because haematocrit primarily reflects your red blood cell mass, the most meaningful lifestyle influences are those that support healthy red cell production and adequate plasma volume.
- Stay well hydrated. Plasma volume directly affects your haematocrit reading. Drinking enough fluid throughout the day — typically around 6–8 glasses according to NHS guidance — helps ensure your result reflects your true red cell mass rather than a dehydration artefact.
- Optimise iron intake. Iron is the essential building block of haemoglobin inside each red blood cell. Eating iron-rich foods regularly and pairing non-haem iron sources with vitamin C can meaningfully improve iron absorption, particularly for people at higher risk of deficiency.
- Ensure adequate B12 and folate. Both nutrients are required for normal red cell maturation. People following a plant-based diet, older adults, and those with absorption issues are at greater risk of deficiency and may benefit from dietary attention or supplementation discussed with a GP.
- Limit alcohol. Heavy alcohol intake impairs the bone marrow's ability to produce red blood cells and can also worsen nutritional deficiencies that drive anaemia. Keeping within the UK Chief Medical Officers' low-risk guideline of no more than 14 units per week is a sensible target.
There is good supporting evidence that the following foods help maintain healthy red blood cell production and a normal haematocrit.
Red meat and offal (e.g. liver)
Among the richest sources of haem iron, the form most readily absorbed by the human gut. Liver is also an excellent source of vitamin B12 and folate.
Legumes (lentils, beans, chickpeas)
Good plant-based sources of non-haem iron and folate; absorption is enhanced when eaten alongside vitamin C-rich foods.
Dark leafy greens (spinach, kale, spring greens)
Provide non-haem iron and folate, both critical for red cell production, and are a staple of an anaemia-protective diet.
Fortified breakfast cereals
Many UK cereals are fortified with iron and B vitamins including folate, making them a practical everyday contribution to red cell nutrition, especially for those with lower meat intake.
Oily fish and eggs
Both are reliable dietary sources of vitamin B12, deficiency of which leads to megaloblastic anaemia and a falling haematocrit.
Citrus fruit and berries
Rich in vitamin C, which significantly enhances the absorption of non-haem iron from plant foods when eaten at the same meal.
Track your own Haematocrit
Upload a lab PDF and Better Days trends Haematocrit over time, flags it when it drifts, and suggests foods that help.
More in Blood Count
Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.