High Haemoglobin on Your Blood Test
What an elevated haemoglobin or Hgb result usually means, the common and the rare causes, and when it is worth seeing your doctor promptly, in plain English.
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· · Reviewed against the sources listed at the end of this page.
The Quick Answer
Haemoglobin (Hgb) is the protein in your red blood cells that carries oxygen around your body. Typical adult ranges are roughly 130-170 g/L(13.0-17.0 g/dL) for men and 115-160 g/L (11.5-16.0 g/dL) for women, though your own lab's printed range may differ slightly.
In the vast majority of cases, a high haemoglobin has a simple, largely reversible explanation: dehydration, smoking, living at altitude, or testosterone therapy. Obstructive sleep apnoea is another common contributor. A bone marrow condition called polycythaemia vera is a genuine but rare cause, usually only considered once the common explanations have been ruled out.
What Is Haemoglobin, and Why Would It Go Up?
Haemoglobin is the iron-containing protein packed inside every red blood cell that binds oxygen in your lungs and releases it to your tissues. A full blood count reports it as grams per litre (g/L) in Australia, or grams per decilitre (g/dL) in the United States and some other countries (roughly 10x smaller number, same concentration).
Haemoglobin can be high for two very different reasons. The first is a smaller volume of plasma (the liquid part of blood) concentrating the same number of red cells, most often from dehydration. The second is your bone marrow genuinely producing more red blood cells, usually because the body senses it needs more oxygen-carrying capacity, for example from smoking, altitude, sleep apnoea, or testosterone. A closely related measurement, haematocrit, reports the proportion of blood volume taken up by red cells and tends to rise and fall alongside haemoglobin for the same reasons.
The word doctors use for a genuinely raised red cell count is polycythaemia. When it happens for an identifiable, external reason, it is called secondarypolycythaemia. When the bone marrow itself is overproducing cells independent of any outside trigger, it is called polycythaemia vera, a rare blood disorder.
Causes of High Haemoglobin
Listed roughly from most to least common. The first four explain the large majority of elevated haemoglobin results seen in general practice.
Dehydration
Not enough fluid in the blood concentrates the same number of red cells into a smaller volume of plasma, so the haemoglobin per litre looks high even though your body has not made extra red cells. Often called relative polycythaemia. A repeat test after normal fluid intake usually settles it.
Smoking
Carbon monoxide from cigarette smoke binds red blood cells and lowers the oxygen they can carry. The bone marrow responds by making more red cells to compensate, which raises haemoglobin. Usually improves within weeks to months of quitting.
Living at altitude
Less oxygen in thinner mountain air means the body makes more red blood cells to carry enough oxygen. This is a normal physiological adaptation, not a disease, and settles if you move back to a lower altitude.
Testosterone therapy
Testosterone directly stimulates red blood cell production in the bone marrow. Injectable testosterone raises haemoglobin more than gels or patches. This is now one of the most frequent causes of a high haemoglobin or haematocrit seen in general practice, and it is closely monitored by prescribing doctors.
Obstructive sleep apnoea
Repeated drops in blood oxygen overnight trigger the same compensatory response as altitude. Often comes with snoring, daytime tiredness, and a thick neck or larger body habitus. Improves with CPAP treatment.
Chronic lung disease (COPD, severe sleep-disordered breathing)
Long-term low blood oxygen from lung disease drives the bone marrow to make more red cells, similar to altitude, but the underlying lung condition itself needs separate management.
Heart disease with low blood oxygen
Certain congenital heart conditions that allow oxygen-poor blood to bypass the lungs can cause chronically low oxygen levels and a compensatory rise in haemoglobin, usually recognised well before adulthood.
Diuretic medications
Water tablets (diuretics) reduce plasma volume and can mimic dehydration, mildly raising the haemoglobin concentration without any increase in actual red cell mass.
Kidney or liver tumours that secrete erythropoietin
A small number of kidney tumours, liver tumours, and some other growths can secrete extra erythropoietin (the hormone that drives red cell production), causing secondary polycythaemia. Usually investigated with imaging if other causes are excluded.
Polycythaemia vera (JAK2-related)
A bone marrow condition where red cells (and often white cells and platelets) are overproduced independent of oxygen levels, caused by a JAK2 gene mutation in the great majority of cases. Confirmed with an EPO level and JAK2 test, managed by a haematologist.
Symptoms That Can Accompany High Haemoglobin
Most people with a mildly high haemoglobin feel completely well and only find out from a routine blood test. Symptoms become more likely as the level rises further, because thicker blood flows less easily through small vessels.
No symptoms at all
The most common scenario. Mildly elevated haemoglobin, especially from dehydration or smoking, is often picked up incidentally on a routine blood test with no symptoms whatsoever.
Headaches
Thicker blood flows less easily through small vessels, which can cause a dull, persistent headache. Usually improves once the underlying cause is treated.
Dizziness or light-headedness
Related to changes in blood flow and viscosity, particularly with higher haemoglobin levels.
Ruddy or flushed complexion
A reddish-purple tinge to the face, palms, or lips, sometimes called plethora, reflects the higher concentration of red blood cells near the skin surface.
Itching after a hot shower or bath (aquagenic pruritus)
A fairly specific and well recognised symptom of polycythaemia vera, thought to relate to histamine release triggered by warm water. Worth mentioning to your GP if it happens repeatedly.
Tinnitus or blurred vision
Thickened blood can affect blood flow to the inner ear and retina, occasionally causing ringing in the ears or visual disturbance.
Calf swelling, pain, or redness
A possible sign of a deep vein thrombosis (blood clot). Thicker blood clots more readily. Needs same-day medical assessment.
Sudden chest pain or breathlessness
Could indicate a pulmonary embolism (a clot that has travelled to the lungs) or a cardiac event. This is a medical emergency, call 000.
Red Flags, When to See a Doctor Promptly
Most people with a high haemoglobin can wait for their next routine GP appointment. But a few combinations of findings deserve a same-day call to your GP, or an emergency department visit if severe:
Calf pain, swelling, or redness
Possible deep vein thrombosis. Thickened blood raises clotting risk. See a doctor the same day, or go to an emergency department if the leg is significantly swollen or hot.
Sudden chest pain, breathlessness, or coughing blood
Could indicate a pulmonary embolism or a cardiac event. Call 000 immediately, do not wait for a GP appointment.
Severe or new headache with visual changes
Very high haemoglobin can thicken blood enough to affect blood flow to the brain and eyes. Needs prompt medical assessment.
Itching after hot water plus a ruddy complexion
This combination is a recognised pattern seen with polycythaemia vera. Worth specifically mentioning to your GP rather than dismissing as dry skin.
Haemoglobin persistently very high despite normal hydration and no smoking
When the common, easily explained causes are ruled out and the level stays high, further investigation for sleep apnoea, lung or heart disease, or polycythaemia vera is warranted.
High haemoglobin while on testosterone therapy, with symptoms
If you are on TRT and develop headaches, visual changes, or clotting symptoms, contact your prescriber promptly. Dose adjustment or venesection may be needed sooner than your next scheduled review.
What Your GP Will Do Next, the Workup
Australian GPs follow a fairly logical sequence when investigating a high haemoglobin, starting with the simple explanations and only moving to specialist tests if those do not fit.
Repeat the full blood count
A single high haemoglobin reading is often repeated to confirm it is not a one-off, particularly if you were unwell, exercising heavily, or poorly hydrated when the first sample was taken.
Review hydration, smoking, and altitude
Your GP will ask about fluid intake in the days before the test, current smoking status, and whether you live or have recently travelled to altitude. These three explain the large majority of mildly high results.
Check for testosterone therapy or other medications
If you take testosterone (prescribed or otherwise), the dose, formulation, and injection frequency are reviewed. Diuretics and some other medications are also checked.
Assess oxygen levels
A pulse oximetry reading or arterial blood gas can show whether chronically low blood oxygen (from lung disease, heart disease, or sleep apnoea) is driving the bone marrow to overproduce red cells.
Consider a sleep study
If snoring, witnessed pauses in breathing, or daytime sleepiness are present, a sleep study can diagnose obstructive sleep apnoea, a common and treatable cause.
Kidney and liver function, and abdominal imaging if needed
Used to look for the rare erythropoietin-secreting tumours, and to check overall organ health, particularly if no other cause is found.
Erythropoietin (EPO) level and JAK2 mutation test
Reserved for cases where the common causes have been excluded or the haemoglobin is very high. A low EPO level with a positive JAK2 mutation supports a diagnosis of polycythaemia vera; this pathway is usually coordinated with a haematologist.
Treatment, What Happens Once the Cause Is Known
Dehydration
No specific treatment beyond drinking normally. Your GP may simply repeat the full blood count in a few weeks once you are well hydrated, rather than proceeding to further tests.
Smoking
Quitting is the treatment. Haemoglobin related to smoking typically improves over weeks to a few months. Your GP or pharmacist can discuss nicotine replacement therapy and other quit-smoking supports, and Quitline (13 7848) offers free ongoing coaching.
Testosterone therapy
Your prescriber may lower the dose, switch from injections to a gel or patch, extend the interval between injections, or arrange periodic venesection (removing a unit of blood, similar to donating blood) to keep haematocrit in a safer range. Do not adjust a prescribed dose yourself, raise it with the doctor managing your therapy.
Obstructive sleep apnoea
Continuous positive airway pressure (CPAP) therapy, and in some cases weight management or a dental appliance, treats the underlying low overnight oxygen levels. Haemoglobin often falls back into range over a few months of consistent CPAP use.
Polycythaemia vera
Managed by a haematologist. Treatment commonly includes regular venesection to keep the haematocrit below a target set by your specialist, low-dose aspirin to reduce clotting risk, and, for higher-risk patients, medication such as hydroxyurea to reduce the marrow's overproduction of blood cells. It is a chronic condition that is actively managed rather than cured, and most people do well with ongoing specialist follow-up.
Practical Steps While You Wait for Answers
Drink normally in the days before a repeat test
If dehydration is suspected, your GP may simply ask you to hydrate well and repeat the full blood count in a few weeks rather than launching straight into further tests.
Stop smoking
Haemoglobin related to smoking typically starts improving within weeks of quitting, alongside the much larger cardiovascular and cancer risk reduction. Ask your GP or pharmacist about quit-smoking support (Quitline 13 7848).
Get sleep apnoea assessed and treated
If you snore heavily, wake unrefreshed, or a partner has noticed pauses in your breathing overnight, ask about a sleep study. CPAP treatment often lowers haemoglobin back into range over a few months.
Discuss testosterone dose and monitoring with your prescriber
Do not stop or change a prescribed testosterone dose yourself. Your prescriber may adjust the dose, switch formulation, or arrange periodic venesection based on your haematocrit trend.
Stay well hydrated generally, especially in hot weather or with exercise
Chronic mild dehydration from inadequate daily fluid intake is a very common and completely reversible contributor.
Keep follow-up blood tests on schedule
Whatever the cause, haemoglobin is usually rechecked periodically so you and your doctor can see the trend over time rather than reacting to a single number.
Sources and reference ranges
Adult reference ranges on this page follow the AACB and RCPA harmonised reference intervals unless stated otherwise; the range printed on your own report always takes precedence because laboratories differ.
- healthdirect Australia: iron studies
- Pathology Tests Explained (Australasian Association for Clinical Biochemistry and Laboratory Medicine)
- Australasian Association for Clinical Biochemistry and Laboratory Medicine, publisher of the harmonised reference intervals
- healthdirect Australia: full blood count
High Haemoglobin, Frequently Asked Questions
What does it mean if my haemoglobin is high?
High haemoglobin means you have more haemoglobin in each litre of blood than the typical adult range, usually above about 170 g/L in men or 160 g/L in women (ranges vary between labs). The most common reasons are simple and reversible: dehydration concentrates the blood, smoking raises haemoglobin because the body compensates for carbon monoxide, and living at altitude does the same because there is less oxygen in the air. Less commonly, testosterone therapy, sleep apnoea, or lung and heart conditions push haemoglobin up. A blood disorder called polycythaemia vera is a rare cause.
What is a normal haemoglobin range in Australia?
Typical adult reference ranges are roughly 130-170 g/L for men and 115-160 g/L for women, though every Australian lab prints its own range on the report and yours may differ slightly. Haemoglobin is naturally a little higher in men, in people who smoke, and in people who live at higher altitude, and slightly lower in pregnancy.
Can dehydration cause high haemoglobin?
Yes, and it is one of the most common causes of a mildly elevated haemoglobin result. When you are dehydrated, the fluid (plasma) part of your blood shrinks while the number of red blood cells stays the same, so the concentration of haemoglobin per litre goes up even though your body has not actually made more red blood cells. This is sometimes called relative or spurious polycythaemia. Drinking normally for a day or two before a repeat test often brings the result back into range.
Does testosterone therapy raise haemoglobin?
Yes. Testosterone stimulates the bone marrow to make more red blood cells, and this is now one of the most common causes of elevated haemoglobin and haematocrit seen in clinical practice, particularly with testosterone replacement therapy (TRT) and even more so with injectable testosterone compared with gels or patches. Doctors monitor haematocrit regularly during testosterone therapy and may lower the dose, space out injections, or arrange venesection (a blood donation-style procedure) if it climbs too high.
Is high haemoglobin from smoking dangerous?
Smoking causes carbon monoxide to bind red blood cells, reducing the oxygen they can carry. Your body responds by making more red blood cells to compensate, which raises haemoglobin. This adaptation, combined with the direct effects of smoking on blood vessels, thickens the blood and adds to the cardiovascular risk that smoking already carries. It is one of the more common reasons haemoglobin is mildly elevated, and it improves after quitting.
What is polycythaemia vera?
Polycythaemia vera (PV) is a rare bone marrow condition in which the marrow makes too many red blood cells (and often too many white cells and platelets too) independent of the usual oxygen-driven signals. It is caused by a mutation, most often in the JAK2 gene, and is diagnosed with specific blood tests including a JAK2 mutation test and an erythropoietin (EPO) level, usually arranged by a haematologist. PV is far less common than the reversible causes above but is important to rule out when haemoglobin is very high or when the common causes have been excluded.
What symptoms come with high haemoglobin?
Many people with mildly high haemoglobin have no symptoms at all. When haemoglobin is higher, thickened blood can cause headaches, dizziness, blurred vision, tinnitus (ringing in the ears), a ruddy or flushed complexion, and itching after a hot shower (called aquagenic pruritus, a fairly specific clue for polycythaemia vera). Because thicker blood is more prone to clotting, some people notice symptoms of a blood clot such as calf swelling and pain or sudden chest pain and breathlessness, which need urgent attention.
What tests come after a high haemoglobin result?
Your GP will usually repeat the full blood count first to confirm the result, then review your hydration, smoking status, medications (including any testosterone therapy) and altitude of residence. If a reversible cause is not obvious, tests commonly ordered include oxygen saturation or an arterial blood gas, a sleep study if sleep apnoea is suspected, kidney and liver function tests, and, if the picture still is not explained, an erythropoietin (EPO) level and JAK2 mutation test to check for polycythaemia vera.
Related Reading
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This page provides general educational information about elevated haemoglobin and polycythaemia. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your GP about abnormal blood test results, they have access to your full medical history and can interpret your results in context. SmarterBlood does not provide medical care.