Haematocrit (HCT)
Haematocrit / Packed Cell Volume
What this test measures
Haematocrit measures the percentage of your blood that is made up of red blood cells. It helps assess anaemia and other blood conditions.
Understanding the numbers
Typical range: Men: 40-52% | Women: 36-48%
Haematocrit is closely related to haemoglobin. Both are measured in a full blood count.
- Low (anaemia): 20–36 %
- Normal (women): 36–48 %
- Upper overlap (men): 48–52 %
- High: 52–60 %
Key numbers
- 36 % — Women — lower limit
- 40 % — Men — lower limit
- 52 % — Men — upper limit (above = polycythaemia)
Typical UK laboratory reference ranges. Haematocrit tracks haemoglobin closely — it rises in dehydration and polycythaemia and falls in anaemia. A persistently high haematocrit with no obvious cause warrants investigation for polycythaemia vera.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean
- Your blood has a higher concentration of red cells
- Can be caused by dehydration (most common)
- Living at high altitude or smoking can raise it
- Rarely, a bone marrow condition called polycythaemia
Questions you could ask your GP
- Is my haematocrit showing signs of anaemia?
- Do I need further tests to find the cause?
- Could dehydration be affecting my result?
- What treatment might I need?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Low haematocrit, heavy periods
Leanne's haematocrit was 30% and her haemoglobin was 98 g/L. Ferritin was 8. She had heavy periods for three years.
What the GP said: “This tracks with your low haemoglobin — the two usually move together. Iron replacement and treating the heavy bleeding is the plan.”
What happened next: After a Mirena coil and iron, her haematocrit was 40% at six months.
Haematocrit adds little to haemoglobin on its own — they tell the same story. Useful when haemoglobin is borderline and you want extra confirmation of anaemia or polycythaemia.
Dehydrated — spuriously high haematocrit
Harbinder had two days of diarrhoea and vomiting. His haematocrit was 52% at presentation.
What the GP said: “Your red cells are too concentrated because of dehydration. This isn't polycythaemia — once we rehydrate, the haematocrit will come back to baseline.”
What happened next: After rehydration Harbinder's repeat haematocrit was 44%.
A raised haematocrit during acute illness is usually just dehydration. Repeat when fluid status is normal before investigating further.
Persistent high haematocrit — polycythaemia vera
Paul's haematocrit was 57% on three occasions over two months. He had itching after a hot shower and occasional headaches.
What the GP said: “A persistent haematocrit above 52% in men, with itching, raises the possibility of polycythaemia vera. I'll check a JAK2 mutation and refer to haematology.”
What happened next: JAK2 was positive. Paul was started on aspirin and venesection, keeping his haematocrit under 45%.
A persistently raised haematocrit is the hallmark of polycythaemia vera — treatable, but important because of stroke and clot risk.
Smoker — secondary polycythaemia
June's haematocrit was 55%. She smoked 25 a day and had known COPD.
What the GP said: “Your body is making extra red cells to cope with lower oxygen levels — this is secondary polycythaemia from smoking and lung disease. The best treatment is stopping smoking; we can also use venesection if it rises higher.”
What happened next: June used a stop-smoking service and varenicline. Six months smoke-free, her haematocrit was 48%.
A high haematocrit in a smoker or someone with lung disease is usually the body's response to low oxygen, not a bone marrow problem. Stopping smoking often brings it down.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.