Hematologist
CION Cancer Clinics
High haemoglobin: primary or secondary? | CION Cancer Clinics
Most high haemoglobin results are secondary. Smoking, sleep apnoea, lung or heart disease, dehydration and testosterone push red cells up, and the count usually settles once the cause is treated. Less often the marrow itself is overproducing, which is primary polycythaemia, or polycythaemia vera. This page explains the common causes, the clues and tests that tell them apart, and when a haematologist should see you. At CION Cancer Clinics, every leukaemia, MDS and MPN case is reviewed by our haematologist and discussed at a tumour board before a plan is agreed.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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The short answer
Why is my haemoglobin high?
Most high haemoglobin results are not caused by a marrow disease. The usual reasons are smoking, low oxygen from a lung or sleep problem, dehydration, or medicines such as testosterone.
Three kinds of high haemoglobin
Doctors sort a high result into three groups. Relative means the red cells are normal but the watery part of the blood has shrunk, often from dehydration or water tablets. Secondary means the body is making extra red cells on purpose, because something is telling it to. Primary means the marrow itself is overproducing, as in polycythaemia vera.
Why the difference matters
Each group is handled differently. Relative polycythaemia often corrects with fluids and a repeat test. Secondary polycythaemia is managed by treating the cause, such as stopping smoking or treating sleep apnoea. Primary polycythaemia needs a haematologist and long-term follow-up, because it raises the risk of clots.
Who usually finds this on a report
Often it is a man in his forties or fifties who had a health check before a job, a visa or an insurance policy. Sometimes it is a parent whose son or daughter spotted the flag while collecting the report. Either way, the high number is a reason to look further, calmly, not a diagnosis by itself.
Reference ranges differ between laboratories. A single high result is read alongside your symptoms and a repeat test, never on its own.Common causes
What pushes haemoglobin up, apart from the marrow?
These are checked before anyone suggests a blood cancer. More than one can be present in the same person.
Smoking and tobacco
Carbon monoxide from cigarettes, beedis and hookah takes the place of oxygen in the blood. The kidneys respond by asking for more red cells. It is one of the most common reasons for a mildly high count.
Low oxygen at night
Sleep apnoea, where breathing stops and starts during sleep, lowers oxygen for hours each night. Loud snoring, daytime sleepiness and morning headaches are clues.
Also in this group
- Long-standing lung disease
- Some heart conditions
- Living at high altitude
Medicines and hormones
Testosterone injections or gels, anabolic steroids used for bodybuilding, and erythropoietin all raise red cells. Tell your doctor about any supplement bought at a gym.
Kidney and liver problems
Cysts or growths in the kidney, a kidney transplant, and some liver conditions can release too much of the hormone that drives red cell production.
Dehydration
Heat, vomiting, loose motions, water tablets or simply drinking too little before a morning test can concentrate the blood. This is the relative type.
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Which clues point to primary or secondary?
Points towards secondary
Points towards primary (polycythaemia vera)
Only the haemoglobin and haematocrit are high
White cells or platelets are also raised
Erythropoietin hormone level is normal or high
Erythropoietin level is low
JAK2 gene test is negative
JAK2 gene test is positive
Smoker, snorer, lung disease or on testosterone
Itching after a bath, burning fingers, enlarged spleen
The usual order
What tests will the doctor ask for?
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A repeat full blood count
Taken after you have drunk normally, ideally at the same laboratory. Many mildly high results settle on a repeat.
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History and examination
Questions about smoking, snoring, breathlessness, medicines and gym supplements. The doctor also feels for an enlarged spleen.
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Oxygen level and simple checks
A finger probe for oxygen, kidney and liver tests, and sometimes a chest X-ray or a sleep study if apnoea is suspected.
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JAK2 test and erythropoietin
If the count stays high with no clear cause, these two blood tests help separate a marrow problem from a reaction to something else.
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Scans or a marrow sample, if needed
An ultrasound of the abdomen checks the kidneys and spleen. A bone marrow biopsy is kept for cases where the answer is still unclear.
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When a high count cannot wait
Thick blood can clot. Sudden weakness or numbness on one side, a drooping face, slurred speech, chest pain, sudden breathlessness, or a painful swollen leg needs emergency care now. Call 108 or go to the nearest emergency department. Do not wait for the blood report appointment first.
Commonly believed
What do people often believe about high haemoglobin?
"High haemoglobin means I have blood cancer."
Most people with a high result do not. Smoking, sleep apnoea, dehydration and testosterone are far more common causes. A marrow disease is considered only once those have been looked at.
"More haemoglobin is always a good sign."
Low haemoglobin gets most of the attention, so a high number can feel like good news. Above the normal range, the blood thickens and the chance of a clot rises, whatever the cause.
"Secondary polycythaemia is harmless, so it can be ignored."
The count itself may be less risky than in polycythaemia vera, but the cause often is not. Untreated sleep apnoea, lung disease or a kidney growth all need their own attention.
"Giving blood regularly will sort it out."
Removing blood without knowing the cause can hide the real problem and lower oxygen delivery in people with lung or heart disease. Any blood removal is a medical decision made by your treating doctor.
Being straight with you
What can this page not tell you?
This page cannot tell you which group your result belongs to. That needs a repeat count, your history and, often, a couple of specific tests read together.
It cannot rule anything in or out
A secondary cause does not exclude polycythaemia vera, because a smoker can also have a marrow condition. A negative JAK2 test makes polycythaemia vera much less likely, but a small group of people carry a different gene change. Your doctor decides how far to look.
It cannot tell you your risk
Clot risk depends on the cause, how high the count is, your age, blood pressure, sugar, cholesterol and any clot you have had before. Only your treating doctor can weigh those together for you.
What to take to the appointment
Bring every blood report you have, in date order, including older ones from health check packages or pre-surgery tests. A rising trend over years tells a different story from one high reading. Write down your medicines and supplements, and whether you smoke or snore. If the count stays high, your GP or physician can refer you to a haematologist, who looks at the whole picture before any label is used.
Do not start water tablets, iron or blood thinners to change the number yourself. Each can make things worse.Questions we are asked
Common questions about high haemoglobin
Can dehydration really make my haemoglobin look high?
Yes. When the body is short of water, the liquid part of the blood shrinks while the red cells stay the same, so the result reads high. This is common after a hot day, a stomach upset or fasting before a test. Drink normally and repeat the count before drawing any conclusion.
Will my haemoglobin come down if I stop smoking?
If smoking is the main cause, it usually falls over the following months once carbon monoxide levels drop. Stopping also lowers your clot and heart risk directly. If the count stays high after you have stopped for a while, your doctor will look for another reason.
I take testosterone. Should I stop it?
Do not stop or change it on your own. Talk to the doctor who prescribed it and share the blood report. They may adjust the plan, check the count more often, or refer you. If the testosterone was bought without a prescription, tell your doctor honestly so the result can be read correctly.
What is the JAK2 test and why was it ordered?
It is a blood test that looks for a gene change found in most people with polycythaemia vera. It is ordered when a high count has no clear outside cause. A positive result points towards the marrow. A negative result makes a marrow cause less likely but does not settle the question alone.
Does secondary polycythaemia need a haematologist?
Not always. Many people are managed by a physician, chest doctor or sleep specialist who treats the underlying cause. A haematologist is usually involved when the cause is unclear, the count is very high, other blood counts are abnormal, or a clot has already happened.
Can high altitude or travel affect the result?
Living at high altitude raises red cells because the air holds less oxygen. A short trip usually does not change a blood count much. Long flights and long road journeys matter more for clots than for the number, so walk about and drink water on the way.
Is a high haematocrit the same as high haemoglobin?
They move together but measure different things. Haemoglobin is the oxygen-carrying protein. Haematocrit, sometimes written PCV, is the share of the blood made up of red cells. Doctors look at both, and the haematocrit is often the number treatment decisions follow.
Can CION look at my report?
Yes. Share your reports through the helpline and the haematology team will review them, suggest which tests are sensible next, and explain whether a haematology appointment is needed. Where specialist tests are required, the team coordinates them with qualified centres and tells you what to ask.
Your Haematologist
Meet CION's haematologist. One specialist for your blood report and your plan.
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
- 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
Polycythaemia Vera ExplainedIf the marrow turns out to be the causeJAK2 Mutation Testing: What a Positive MeansThe gene test that separates primary from secondaryJAK2 Negative but Counts Still HighWhat happens when the gene test comes back negativeBlood cancer guideAn overview of the wider family of blood cancers
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Haemoglobin higher than it should be?
Share your reports with us. CION's haematology team will read them and tell you which test is sensible next. One helpline serves every CION centre.