Are my haemoglobin and haematocrit high?
Yes, if they’re above the range on your sheet. But UK blood specialists trust one of these two lines more. And their trigger for more tests is a result that stays high.
On this page
Is my Hb blood test high?
It is if it sits above the range printed next to it. At one NHS lab, haemoglobin (Hb) tops out at 180 g/L for men and 165 for women. Haematocrit (Hct) tops out at 0.54 and 0.47.
Haematocrit is the space your red cells take up in your blood. Doctors use both lines as a stand-in for how many red cells you have.
| Line | Men | Women |
|---|---|---|
| Haemoglobin (Hb) | 130 to 180 g/L | 115 to 165 g/L |
| Haematocrit (Hct) | 0.40 to 0.54 | 0.37 to 0.47 |
Source: Gloucestershire Hospitals NHS
US results use different units. Divide a UK g/L number by 10 to get g/dL, so 180 g/L is 18.0 g/dL. A haematocrit of 0.54 is the same as 54%.
Your next move: find both lines on your sheet and note the range beside each. Ranges differ a little between labs.
High haemoglobin and haematocrit: which matters more?
UK blood specialists, the British Society for Haematology (BSH), lean on one line. That line is your haematocrit. They say it spots a true excess of red cells better than haemoglobin does.
Their trigger for more tests is a haematocrit that stays above 0.52 in men or 0.48 in women. The key word is stays.
- Below 40 %Below this lab’s range.
- 40 up to 52 %In range. Not above the BSH line.
- Above 52 up to 54 %In range, but above the BSH line. Matters if it stays.
- Above 54 up to 60 %Above the range and the BSH line.
- Above 60 %BSH: a true excess of red cells can be assumed.
Sources: BSH guideline; Gloucestershire Hospitals NHS
- Below 37 %Below this lab’s range.
- 37 up to 47 %In range.
- Above 47 up to 48 %Above this lab’s range. Not above the BSH line.
- Above 48 up to 56 %Above the BSH line. Matters if it stays.
- Above 56 %BSH: a true excess of red cells can be assumed.
Sources: BSH guideline; Gloucestershire Hospitals NHS
Above 0.60 in men or 0.56 in women, BSH says doctors can assume a true excess of red cells. Below that, a special test of red cell mass can help confirm it.
Your next move: compare your haematocrit with the line for your sex, not just the lab range.
What causes elevated haemoglobin and haematocrit?
Both lines can rise two ways. Your body makes more red cells, or your blood holds less of the fluid they float in (plasma).
| What’s going on | Common causes |
|---|---|
| Less fluid in your blood | Dehydration. Also being overweight, smoking, drinking too much alcohol or water tablets (diuretics). |
| Low oxygen | Long-term lung disease such as COPD (lung damage that makes it hard to breathe out), sleep apnoea (breathing that stops and starts in sleep), smoking or living at altitude. |
| Medicines and drugs | Testosterone, growth hormone, EPO (a hormone that boosts red cells) and water tablets. |
| Kidney problems | Such as narrowed kidney arteries, kidney cysts or kidney cancer. |
| Bone marrow | Polycythaemia vera, a rare, slow-growing blood cancer. The average age at diagnosis is 60. |
Sources: NHS: erythrocytosis; BSH guideline
With low oxygen or some kidney problems, your kidneys make more of a hormone that tells your bone marrow to make red cells. In some people, no cause is found.
Snore and feel tired in the day? See our sleep apnoea guide.
On testosterone? See our TRT blood test guide.
Drank little before the test? Read about dehydration and blood test results.
Your next move: note which of these could apply to you.
What happens after a high Hb blood test?
It is sometimes only found on a routine test done for another reason. BSH says doctors should look closely at medicines, recreational drugs, smoking, alcohol and body size.
What can happen after a high haematocrit
- 1
Questions
Your GP asks about medicines, smoking, alcohol, weight and symptoms.
- 2
Clear cause
If the cause is clear, you may not need more tests.
- 3
Specialist
If not, your GP may refer you to a blood specialist (haematologist).
- 4
More tests
These may include a blood test for a change in a gene called JAK2 or a scan of your tummy to check your kidneys.
Sources: BSH guideline; NHS: erythrocytosis
Before your GP appointment
- Note if you drank little or were dehydrated before the test.
- Write down any headaches, blurred vision, dizziness, red skin or itching after a bath or shower.
- Say if you smoke, how much alcohol you drink, and if you have a lung or kidney condition.
- List every medicine you take, including water tablets, testosterone and any recreational drugs.
- Ask for your full results, including haematocrit, white cells and platelets.
Sources: NHS: erythrocytosis; BSH guideline
White cells and platelets matter because in polycythaemia vera they can be high too. Our full blood count guide explains every line.
Your next move: take the checklist above to your GP appointment.
Never stop or change a prescribed medicine without your prescriber.
Is high haemoglobin dangerous?
Often not. The NHS says many cases are mild and may not lead to any further complications.
But too many red cells make blood thicker and less able to flow. Think of honey through a straw instead of water.
Thick blood doesn’t mean a clot will happen. It does make clots, heart attack and stroke more likely. Smoking and being overweight raise the clot risk further.
Stopping smoking or cutting down on alcohol may help when less fluid is the cause. If well controlled, the NHS says it should not affect your life expectancy. Some cases, mainly polycythaemia vera, are more serious and need long-term treatment, and can slightly shorten life expectancy.
Your next move: learn the clot signs in the next section.
When to speak to a GP
Some of these need a GP appointment. Others need help straight away.
- Book a GP appointment if you have symptoms that won’t go away: headaches, blurred vision, red skin on your face, hands or feet, tiredness, high blood pressure or dizziness.
- The same goes for tummy discomfort, confusion, nosebleeds or bruising, gout (painful, swollen joints), or itchy skin after a bath or shower.
- Get medical help straight away for signs of a clot in a leg: pain, swelling, redness or tenderness, a heavy ache, or warm skin over the area.
- Get help straight away too for breathlessness, chest or upper back pain, coughing up blood, feeling lightheaded or dizzy, or fainting.
Call 999 for emergency help if you think someone is having a heart attack or stroke.
Haemoglobin low instead? See our haemoglobin levels guide.
Red cell count high too? See our high red blood cell count guide.