Is my red blood cell count high?
Yes, if it’s above the range printed beside it. But a high count doesn’t always mean you’re making too many red cells. Sometimes your blood is just short of fluid.
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Is my RBC count high?
It is if it sits above the range printed next to it. One NHS lab tops out at 6.0 for men and 5.3 for women. Another goes up to 6.5 and 5.8.
The unit, x10¹²/L, means trillions of red cells in each litre of blood.
- Below 4.5 x10¹²/LBelow both labs’ ranges.
- 4.5 up to 6 x10¹²/LIn range at both labs.
- Above 6 up to 6.5 x10¹²/LAbove one lab’s range, in the other’s.
- Above 6.5 x10¹²/LAbove both labs’ ranges.
Sources: Severn Pathology (North Bristol NHS); Gloucestershire Hospitals NHS
- Below 3.8 x10¹²/LBelow both labs’ ranges.
- 3.8 up to 5.3 x10¹²/LIn range at both labs.
- Above 5.3 up to 5.8 x10¹²/LAbove one lab’s range, in the other’s.
- Above 5.8 x10¹²/LAbove both labs’ ranges.
Sources: Severn Pathology (North Bristol NHS); Gloucestershire Hospitals NHS
Red cells carry oxygen from your lungs to every cell. Too many of them packed into your blood makes it thicker and slower. Think of rush-hour traffic on a busy road.
Not everyone gets symptoms, but many do, such as headaches, dizziness or blurred vision.
Your next move: check your range, then look at the haematocrit line (how much of your blood is red cells) on the same sheet.
Too many red cells, or too little fluid?
Your count is red cells per litre. So it can rise two ways: more cells, or less of the fluid they float in.
That second way has a name: apparent or relative erythrocytosis. Your body has a normal number of red cells but less fluid (plasma), so the blood is thicker.
| Type | Common causes |
|---|---|
| Less fluid | Dehydration, diarrhoea or burns. Also being overweight, smoking, drinking too much alcohol or water tablets (diuretics). |
| More cells, from another condition or place | Lung disease such as COPD, heart disease, kidney problems, sleep apnoea (breathing that stops and starts while you sleep) or living at high altitude. |
| More cells, from misused drugs | Anabolic steroids misused for sport. |
| More cells, from the bone marrow | Polycythaemia vera, a rare, slow-growing blood cancer. |
Sources: NHS: erythrocytosis; North West London Pathology (NHS); MedlinePlus
With lung disease such as COPD, too little oxygen can reach your body. Your kidneys then release more of a hormone that tells your bone marrow to make red cells. In some people, no cause is found.
Your next move: note which of these could apply to you.
If you snore and feel tired in the day, see our sleep apnoea guide. On testosterone? See our TRT blood test guide.
Slightly elevated red blood cell count
A high count is sometimes only found on a routine blood test done for another reason. The NHS says many cases are mild.
Fluid loss from diarrhoea, dehydration or burns can raise it. More in our guide to dehydration and blood test results.
Check two more lines. Haematocrit is the space your red cells take up in your blood. One NHS lab’s range is 0.40 to 0.54 for men and 0.37 to 0.47 for women.
Then look at white cells and platelets. In polycythaemia vera, both can be high too. See our full blood count guide for every line.
Before your GP appointment
- Note if you were ill, had diarrhoea or drank little before the test.
- Write down any headaches, blurred vision, dizziness, red skin or itching after a bath.
- Say if you smoke, how much alcohol you drink, and if you snore.
- List every medicine you take, including water tablets and any steroids.
- Ask for your full results, including haematocrit, white cells and platelets.
Sources: NHS: erythrocytosis; MedlinePlus
Never stop or change a prescribed medicine without your prescriber.
What happens after a high RBC blood test?
What can happen after a high red cell count
- 1
Questions
Your GP weighs your symptoms, history and other blood results.
- 2
Specialist
Your GP may refer you to a blood specialist (haematologist).
- 3
More tests
These may include a gene test called JAK2, or a scan of your tummy to check your kidneys.
- 4
Treatment
Such as removing blood, medicines or low-dose aspirin, depending on the type.
Sources: NHS: erythrocytosis; MedlinePlus
Removing blood is called venesection. It takes about 1 pint at a time, much like giving blood.
The less-fluid kind (apparent erythrocytosis) may improve once its cause is managed. The NHS says stopping smoking or cutting down on alcohol may help.
Your next move: ask your GP which type they think you have.
Is a high red blood cell count dangerous?
Too many red cells in your blood (erythrocytosis) can cause blood clots. It also raises the risk of heart attack and stroke. Being overweight or smoking adds to the clot risk.
Back to the traffic. Busier roads don’t mean a crash. They do make one more likely.
If it’s well controlled, the NHS says it should not affect your life expectancy. People with polycythaemia vera can live slightly less long, because of the higher risk of heart attack and stroke.
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.
Count low instead? See our low red blood cell count guide.