Hematologist
CION Cancer Clinics
Raised counts in dehydration and altitude | CION Cancer Clinics
Yes, both can raise haemoglobin, in different ways. Dehydration makes it look high because your blood holds less water, and a repeat test after drinking normally usually brings it back into range. Time spent at altitude makes it truly high, because your body builds extra red cells. If the count stays high without either reason, a haematologist should look for the cause. This page explains how. 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
- Can dehydration or altitude make my haemoglobin high?
- What everyday things can push the numbers up?
- How does a doctor tell a concentrated sample from a real rise?
- What do the words on my report mean?
- What do people often misunderstand about high haemoglobin?
- When is it not just water or height, and what can this page not tell you?
- Common questions about dehydration, altitude and haemoglobin
The short answer
Can dehydration or altitude make my haemoglobin high?
Yes, both can. Dehydration makes haemoglobin look high because your blood has less water in it. Living at altitude makes it truly high, because your body builds extra red cells to carry more oxygen.
Two different things with the same result
Dehydration does not add a single red cell. It shrinks the watery part of the blood, called plasma, so the same red cells are packed into a smaller volume. The number goes up on paper. Drink normally for a few days, repeat the test, and the number usually comes back down.
Altitude is different. Thin mountain air carries less oxygen, so the kidneys release a hormone that tells the bone marrow to make more red cells. That rise is real. It builds slowly over weeks at height and fades slowly after you come back down.
What the numbers usually look like
One widely used guide gives a usual adult range of about 13.8 to 17.2 grams per decilitre for men, and 12.1 to 15.1 for women. Ranges differ between laboratories, so always read your result against the range printed on your own report. A single result is read with your symptoms and a repeat test, never on its own.
Everyday causes
What everyday things can push the numbers up?
Several of these are common in Telangana and Andhra Pradesh, especially in the hot months. Tell your doctor about any that apply to the days before your test.
Heat and sweating
Outdoor work, a long commute in summer or a hot kitchen can leave you short of water without feeling very thirsty.
Also think about
- Loose motions or vomiting in recent days
- Fasting, including religious fasts
- A test taken early, before any water
Time at height
A posting in the Himalayas, a long trek, or years spent living in a hill region can raise red cells for real. A short pilgrimage usually changes little.
Medicines that remove water
Water tablets, often given for blood pressure or swelling, can concentrate the blood. Tell your doctor you take them. Do not stop them yourself because of a blood report.
Habits that add to it
Smoking, heavy drinking and being overweight all tend to push haemoglobin up a little, and often sit alongside dehydration.
Smoking and sleep apnoea have their own page in this guide.Not sure whether this applies to you?
Ask an oncologistSorting it out
How does a doctor tell a concentrated sample from a real rise?
Ask about the days before
Heat, illness, fasting, travel to height, smoking and your medicines. Often the story alone explains a borderline result.
Repeat the test well hydrated
Drink normally for a few days and repeat the count. If it falls back into range, dehydration was the likely reason.
Read the other lines
Haematocrit, white cells and platelets are checked too. If they are also high, a marrow cause becomes more likely and needs a closer look.
Look further if it stays high
A persistent rise with no clear reason is referred to a haematologist. Tests may include oxygen levels, kidney checks and a blood test for a gene change called JAK2.
On your report
What do the words on my report mean?
- Haemoglobin (Hb)
- The protein in red cells that carries oxygen. It is measured in grams per decilitre, written g/dL.
- Haematocrit or PCV
- The share of your blood made up of red cells. Dehydration pushes it up along with haemoglobin.
- Relative or apparent polycythaemia
- Red cell numbers look high only because the plasma, the watery part of blood, is reduced.
- Secondary polycythaemia
- A true rise in red cells caused by something outside the marrow, such as low oxygen at altitude.
- Polycythaemia vera
- A rare, slow marrow condition in which red cells are made without the usual signal. It is managed by a haematologist.
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Commonly believed
What do people often misunderstand about high haemoglobin?
"High haemoglobin means very good health."
More is not always better. Blood with too many red cells is thicker and flows less easily, which is why a result above your range is worth a proper check, even when you feel strong.
"Drinking lots of water before the test will fix it."
Drinking normally over a few days gives an honest reading. Forcing litres just before the sample does not change a real rise, and it can hide the trend your doctor is trying to see.
"I can give blood to bring it down."
Removing blood is a medical treatment for some marrow conditions, planned by a haematologist. Donating on your own to lower a number skips the question of why it is high.
"It came back normal once, so the high one was a mistake."
It may well have been dehydration. But if later reports creep up again, show your doctor all of them together. A pattern tells more than any single result.
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When a high haemoglobin cannot wait
Thick blood raises the chance of a clot. If you have a high count and notice sudden weakness or numbness of the face, arm or leg, slurred speech, chest pain, sudden breathlessness, or a painful swollen calf, go to the nearest emergency department now or call 108. Do not wait for a repeat test or an appointment.
Being straight with you
When is it not just water or height, and what can this page not tell you?
If your haemoglobin stays high after you have been drinking normally, and you have not spent time at height, something else needs to be found. That does not mean cancer. Most causes are treatable, and many sit outside the blood altogether.
Signs that point beyond dehydration
Look out for itching after a warm bath, headaches, a red face, burning in the hands or feet, or a swollen tummy on the left side. Raised white cells or platelets on the same report also matter. Any of these is a reason to ask for a haematologist's review.
Who this explanation does not suit
Anyone with a past clot, heart or lung disease, or a count that has been climbing across several reports should not assume dehydration is the answer. Nor should someone whose count stayed high long after coming down from the hills.
What this page cannot do
It cannot tell you which cause applies to you. Please do not change any medicine because of a report. Bring every old result, so the trend is clear.
Questions we are asked
Common questions about dehydration, altitude and haemoglobin
How long after drinking water should I repeat the test?
Your doctor will set the timing. In general, drink your usual amount of fluid for a few days, avoid a long spell in the heat the day before, and have a normal glass of water on the morning of the test. That gives a fairer reading than a single sample taken when you were short of water.
I just came back from a Himalayan trip. Is that why it is high?
Possibly, if you stayed at height for a good while. Short visits usually change little. Tell your doctor how long you spent there and how high. The rise from altitude fades gradually after you return, so a repeat test some weeks later, at your doctor's advice, shows whether it settles.
Can fasting raise haemoglobin on a blood test?
It can, if the fast includes going without water for long hours, especially in hot weather. The effect is from less water in the blood, not more red cells. If your test fell during a fast, mention it and ask whether to repeat the count once you are eating and drinking normally again.
Can a high haemoglobin cause a stroke?
A truly high red cell count makes the blood thicker, which raises the chance of a clot. Mild dehydration on its own is a much smaller concern. If you ever notice sudden weakness, slurred speech or chest pain, treat it as an emergency and call 108 or go to the nearest emergency department.
Is high haemoglobin a sign of blood cancer?
Rarely. Most high readings come from dehydration, smoking, altitude, sleep problems or lung and heart conditions. A marrow condition called polycythaemia vera is one uncommon cause, and it is looked for when the count stays high without a clear reason, or when white cells and platelets are also raised.
Should I stop my water tablets because of this result?
No, not on your own. Water tablets are usually prescribed for a good reason, such as blood pressure or heart trouble. Show the report to the doctor who prescribed them. They can decide whether the medicine is part of the picture and whether anything should change.
Does the heat in Hyderabad really make a difference?
It can. In the summer months, people who work outside, travel long distances or do not drink enough can become mildly dehydrated without noticing. That is enough to nudge haemoglobin and haematocrit upwards. It is one reason a doctor often repeats a borderline result rather than acting on it straight away.
When should I see a haematologist?
See one if your haemoglobin stays above your laboratory's range on repeat tests after drinking normally, if other counts are also high, or if you have itching after bathing, headaches or a past clot. CION's haematology team can review your reports and explain which tests, if any, are needed next.
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
- MedlinePlus, US National Library of Medicine — Hemoglobin
- NHS — Polycythaemia
- NHS — Dehydration
- National Heart, Lung, and Blood Institute — Polycythemia Vera
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
Secondary Polycythaemia: High Haemoglobin With a CauseOther causes of a true red cell riseSleep Apnoea, Smoking and High HaemoglobinTwo common reasons that often sit alongside dehydrationWhen a High Count Needs Marrow TestingWhat decides whether marrow tests are neededRaised Counts and Reactive ChangesThe full guide to high blood counts
Talk to us
Worried about a high haemoglobin result?
Share your reports or call the helpline. CION's haematology team can go through the trend with you and explain whether more testing is needed.