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Secondary polycythaemia: a high haemoglobin with a cause | CION Cancer Clinics
Secondary polycythaemia means your red cell count is high because something outside the bone marrow is driving it. Smoking, sleep apnoea, lung or heart disease, kidney problems and testosterone are the usual causes. The marrow itself is healthy, and the count often settles once the cause is treated. This page explains the causes, how doctors tell it apart from polycythaemia vera, and what happens next. At CION Cancer Clinics, our haematologist reviews abnormal blood reports with you, orders only the tests that answer your question and explains each result plainly.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- What is secondary polycythaemia?
- What usually causes a high haemoglobin with a reason behind it?
- How will the doctor work out which cause you have?
- What do the words on the report mean?
- How is secondary polycythaemia treated?
- What do people often get wrong about a high haemoglobin?
- Common questions about secondary polycythaemia
The short answer
What is secondary polycythaemia?
Secondary polycythaemia means your body is making too many red blood cells because something else is pushing it to. The bone marrow itself is healthy. It is responding to a signal, most often a lack of oxygen, and the count usually settles when that cause is found and dealt with.
How the signal works
Your kidneys watch how much oxygen reaches them. When they sense too little, they release a hormone called erythropoietin, often written EPO on a report. EPO tells the marrow to make more red cells, so that each breath carries more oxygen around the body. That is a sensible response in the short term. When the low oxygen goes on for months, the extra red cells build up and the blood becomes thicker.
Why the word "secondary" matters
It separates this from polycythaemia vera, a slow-growing blood cancer in which the marrow makes too many cells with no outside signal at all. The two can look alike on a single blood count. They are managed very differently, which is why your doctor will want to know which one you have before deciding anything.
Reference ranges for haemoglobin differ between laboratories, and a single result is always read alongside your symptoms and a repeat test.Common causes
What usually causes a high haemoglobin with a reason behind it?
Most causes fall into a few groups. Many people have more than one at the same time, such as smoking and a snoring problem.
Smoking
Cigarette and beedi smoke fill part of the blood with carbon monoxide, which takes the place of oxygen. The kidneys read this as low oxygen and push the red cell count up. It is one of the most common causes seen in men.
Lung and breathing problems
Long-standing lung disease leaves the blood short of oxygen through the day or night.
Often seen with
- COPD, often from smoking or years near a wood or coal chulha
- Obstructive sleep apnoea, where breathing stops during sleep
- Scarring of the lungs after old infections
Heart conditions
Some heart problems present from birth let blood bypass the lungs, so less oxygen gets picked up. The marrow makes more red cells to compensate.
Kidney causes and some growths
Kidney cysts, a narrowed kidney artery, life after a kidney transplant, and some kidney or liver growths can release EPO without any shortage of oxygen.
This is why a kidney scan is sometimes part of the work-up.Testosterone and similar medicines
Testosterone therapy and anabolic steroids used for body-building both raise red cell production. Tell your doctor about any injection or supplement, even one bought at a gym.
Not sure whether this applies to you?
Ask an oncologistFinding the cause
How will the doctor work out which cause you have?
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A repeat blood count
The first step is usually to repeat the test, well hydrated and not straight after smoking. A high result from a day of little water or a fever may simply not come back.
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Questions about your daily life
Expect to be asked about smoking, snoring, daytime sleepiness, breathlessness, medicines, supplements, and whether you have recently lived or trekked at high altitude.
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An oxygen check
A small clip on your finger measures oxygen in the blood. A normal daytime reading does not rule out low oxygen at night, so a sleep study may be suggested if you snore heavily.
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EPO and JAK2 tests
An EPO level that is normal or high points towards a secondary cause. A JAK2 blood test looks for the gene change seen in most people with polycythaemia vera. Together they separate the two in most cases.
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Scans if needed
A chest X-ray, heart scan or kidney ultrasound is added only when the history points that way. A bone marrow test is not usually needed when a clear secondary cause is found.
On your report
What do the words on the report mean?
- Haemoglobin (Hb)
- The protein in red cells that carries oxygen. It is the number most people notice first when it is flagged high.
- Haematocrit or PCV
- The share of your blood made up of red cells. A high value means the blood is thicker than usual.
- RBC count
- The number of red blood cells in a small amount of blood. It often rises alongside haemoglobin.
- Erythropoietin (EPO)
- The kidney hormone that tells the marrow to make red cells. It is usually normal or high in secondary polycythaemia.
- JAK2 mutation
- A gene change found in most people with polycythaemia vera. A negative result makes that condition much less likely.
- SpO2
- Oxygen saturation, the reading from the finger clip. It shows how full of oxygen your red cells are at that moment.
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What happens next
How is secondary polycythaemia treated?
The main treatment is to deal with the cause. When the cause improves, the red cell count usually comes down on its own over the following months.
Treating the cause
Stopping smoking is the single change that helps most smokers. A breathing machine worn at night, called CPAP, treats sleep apnoea and often brings the count down. Lung and heart conditions are managed by the relevant specialist. If testosterone is the cause, talk to the doctor who prescribed it. Do not stop or change it on your own.
Removing some blood
Some people are offered venesection, which means taking off a unit of blood, much like donating it. It thins the blood quickly. It does not suit everyone. If your body raised the count because it genuinely needs the oxygen, as in some lung or heart disease, taking blood off can leave you more breathless. Your treating team decides whether it helps you.
What this page cannot tell you
It cannot tell you which cause you have, or whether your own count needs treating. That depends on your symptoms, the repeat tests and your other health conditions. Bring every report you have to the appointment.
Commonly believed
What do people often get wrong about a high haemoglobin?
"High haemoglobin means strong, healthy blood."
More red cells are not always better. Above the normal range the blood becomes thicker and flows more slowly, which can raise the chance of a clot. A high result deserves a proper look, not a compliment.
"A high count means I have blood cancer."
Most high haemoglobin results in adults have a secondary cause such as smoking, sleep apnoea or dehydration. Polycythaemia vera is far less common. Simple blood tests usually tell the two apart without a marrow test.
"If I just drink more water, it will be fixed."
Water corrects a high count caused by dehydration. It does not fix one driven by low oxygen, smoking or a kidney cause. If the repeat test, done well hydrated, is still high, the cause needs finding.
"Giving blood regularly is a safe way to bring it down."
Blood banks may not accept donors with an unexplained high count, and removing blood without a diagnosis can hide the real cause. Any blood removal should be planned by your treating team.
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Signs that cannot wait
Thick blood can raise the chance of a clot. If you have sudden weakness or numbness on one side, a drooping face, slurred speech, chest pain, sudden breathlessness, or one painful swollen leg, call 108 or go to the nearest emergency department now. Say that your haemoglobin was recently found to be high.
Questions we are asked
Common questions about secondary polycythaemia
Is secondary polycythaemia a type of cancer?
No. In secondary polycythaemia the bone marrow is healthy and is responding to a signal from elsewhere in the body. The blood cancer with a similar name is polycythaemia vera. Your doctor separates the two with an EPO level, a JAK2 test and your history, so ask which tests were done if you are unsure.
Can smoking alone really raise my haemoglobin?
Yes. Carbon monoxide from smoke takes up space on red cells that oxygen should use, and the body responds by making more red cells. Heavy smokers commonly have a raised count. After you stop, the count usually falls gradually. Ask your doctor when a repeat test would be useful.
My father snores loudly and his haemoglobin is high. Could they be linked?
They may be. Loud snoring with pauses in breathing, morning headaches and daytime sleepiness are signs of obstructive sleep apnoea. The repeated dips in oxygen at night can raise the red cell count. A sleep study confirms it, and treating the apnoea often lowers the count as well.
Does a high haemoglobin cause symptoms?
Many people feel nothing and find it on a routine test. Others notice headaches, dizziness, a red face, itching after a warm bath or blurred vision. These symptoms are not specific, so they cannot tell you the cause. Mention them to the doctor reviewing your report.
Will I need a bone marrow test?
Usually not. When there is a clear secondary cause, a normal or high EPO level and a negative JAK2 test, a marrow test adds little. It is considered when the picture does not fit, or when other counts such as platelets or white cells are also raised.
Do I need a blood thinner?
That depends on your overall risk of clots, your other conditions and the cause of the high count. It is a decision for your treating doctor. Do not start aspirin or any blood thinner on your own, because these medicines also carry a risk of bleeding.
Which doctor should I see first?
Your family doctor or a physician can often find the cause. A haematologist, a specialist in blood disorders, is helpful when the cause is unclear, other counts are abnormal, or the JAK2 test is positive. A chest or sleep specialist may be involved for lung problems or sleep apnoea.
Can CION look at my reports?
Yes. Share your blood reports with the helpline and CION's haematology team, led by Dr. Basudev Pokhrel, can review them and suggest which tests make sense next. Where a test or treatment is done elsewhere, the team will tell you what to ask for and help coordinate it.
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Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Sources
- NHS — Polycythaemia
- National Heart, Lung, and Blood Institute — Polycythemia vera
- Leukemia & Lymphoma Society — Polycythemia vera
- NHS — Obstructive sleep apnoea
- National Health Mission — National Health Mission
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Sleep Apnoea, Smoking and High HaemoglobinThe two most common causes, in more detailRaised Counts in Dehydration and AltitudeWhen a high result is about too little water, not too many cellsWhen a High Count Needs Marrow TestingThe signs that point beyond a secondary causeRaised Counts and Reactive ChangesEvery guide on high blood counts in one place
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