High hemoglobin levels can significantly impact your body’s health and daily functioning. When hemoglobin levels exceed normal ranges[1], typically above 17.2 grams per deciliter in men and 15.1 grams per deciliter in women, the body experiences various changes that can range from mild discomfort to serious complications.
A high hemoglobin count can cause headaches, fatigue, dizziness, and increase the risk of dangerous blood clots, heart attacks, and strokes. While some people may not notice any symptoms initially, the condition often develops due to underlying health issues like heart disease, lung problems, or blood disorders that require medical attention.
Understanding what happens when hemoglobin levels rise helps people recognize warning signs and seek appropriate treatment. The effects on the body depend on how high the levels are, what’s causing the increase, and how long the condition has been present. High haemoglobin levels can affect blood circulation[2] and put extra strain on vital organs throughout the body.
Key Takeaways
- High hemoglobin count can cause symptoms like headaches and dizziness while increasing risks of blood clots and heart problems
- The condition often results from underlying health issues such as lung disease, heart problems, or lifestyle factors like smoking
- Treatment focuses on addressing the root cause and may include medications, lifestyle changes, or procedures to remove excess blood
How High Hemoglobin Affects the Body
High hemoglobin creates a cascade of changes throughout the body by increasing blood thickness and altering circulation patterns. These changes put extra stress on the heart and can disrupt normal oxygen delivery to tissues.
Thicker Blood and Hyperviscosity
When hemoglobin levels rise above normal ranges, the blood becomes significantly thicker and more viscous. This happens because high red blood cell counts[1] increase the overall density of blood.
Thickened blood moves more slowly through blood vessels. The increased viscosity makes it harder for blood to flow smoothly through small capillaries and arteries.
Key effects of hyperviscosity include:
- Reduced blood flow velocity
- Increased resistance in blood vessels
- Higher pressure needed to pump blood
- Sluggish circulation in extremities
The body struggles to maintain normal circulation when blood viscosity increases. This creates a domino effect that impacts multiple organ systems and bodily functions.
Blood Flow and Oxygen Delivery Changes
Despite having more red blood cells, high hemoglobin can actually worsen oxygen delivery to tissues. The thicker blood moves too slowly to efficiently transport oxygen where it’s needed most.
Slower blood flow means tissues may not receive oxygen quickly enough. This paradox occurs because circulation speed matters more than just having extra red blood cells.
Common circulation problems include:
- Reduced flow to fingers and toes
- Poor circulation in the brain
- Decreased blood supply to organs
- Impaired nutrient delivery
The body may respond by trying to increase heart rate or blood pressure. These compensatory mechanisms often fail to fully restore normal oxygen delivery patterns.
Cardiovascular Stress and Heart Strain
The heart must work much harder to pump thickened blood through the circulatory system. This increased workload puts significant strain on the cardiovascular system over time.
Higher blood viscosity forces the heart to generate more pressure with each beat. The left ventricle faces the greatest challenge as it pumps blood to the entire body.
Heart-related complications may include:
- Elevated blood pressure
- Irregular heart rhythms
- Enlarged heart chambers
- Increased risk of heart failure
Blood clot formation becomes more likely with high hemoglobin levels[1]. The thick, slow-moving blood tends to clump together more easily in blood vessels.
This cardiovascular stress can lead to serious complications if left untreated. The heart may eventually struggle to maintain adequate circulation throughout the body.
Common Symptoms of High Hemoglobin
High hemoglobin creates thick blood that flows poorly through blood vessels, leading to reduced oxygen delivery despite higher red blood cell counts. Most people experience fatigue, headaches, and dizziness[1] as the primary warning signs.
Fatigue and Weakness
People with high hemoglobin often feel tired even after getting enough sleep. The thick blood moves slowly through blood vessels, making the heart work harder to pump blood throughout the body.
This extra strain on the heart causes persistent exhaustion. Many people describe feeling like they are walking through mud or carrying heavy weights.
The fatigue gets worse during physical activity. Simple tasks like climbing stairs or carrying groceries become much more difficult than usual.
Key fatigue symptoms include:
- Feeling tired all day despite adequate rest
- Weakness in muscles during normal activities
- Need for frequent breaks during light exercise
- Difficulty concentrating due to mental exhaustion
Headaches and Dizziness
High hemoglobin levels can cause headaches[3] because thick blood has trouble reaching small blood vessels in the brain. These headaches often feel different from regular tension headaches.
The pain typically feels like pressure or fullness inside the head. Many people describe it as a constant, dull ache that gets worse when bending over or lying down.
Dizziness symptoms include:
- Feeling lightheaded when standing up quickly
- Room spinning sensation
- Unsteady walking or balance problems
- Feeling faint during normal activities
The dizziness happens because the brain receives inconsistent blood flow. This creates moments where brain cells do not get enough oxygen despite high red blood cell counts.
Blurred Vision and Neurological Signs
High hemoglobin affects small blood vessels in the eyes, causing vision problems. People may notice their eyesight becomes fuzzy or unclear, especially when reading or looking at distant objects.
Vision changes include:
- Difficulty focusing on text or small details
- Double vision episodes
- Temporary blind spots
- Eye strain and discomfort
Thick blood can also cause neurological symptoms. Some people experience tingling in their hands and feet, similar to when a limb “falls asleep.”
Memory problems and confusion may develop as brain blood flow becomes irregular. These symptoms often worsen gradually over time if left untreated.
Excessive Sweating and Itchy Skin
Excessive sweating[1] occurs even in cool temperatures or during rest. The body produces more sweat as it tries to cool down from the extra work of pumping thick blood.
This sweating often happens at night, soaking through pajamas and bedsheets. Many people need to change clothes multiple times during sleep.
Skin symptoms include:
- Intense itching after hot showers or baths
- Red, flushed appearance on face and neck
- Scratching that provides only temporary relief
- Skin that feels warm to the touch
The itchy skin develops because thick blood struggles to flow through tiny blood vessels near the skin surface. This creates inflammation and irritation that feels like constant itching or burning.
Serious Health Risks and Complications
High hemoglobin levels create thick, sticky blood that moves slowly through blood vessels. This increased blood thickness can lead to dangerous clots[1] and serious heart problems.
Blood Clots and Deep Vein Thrombosis
Thick blood from high hemoglobin moves slowly through veins and arteries. This slow movement makes blood clots more likely to form.
Deep vein thrombosis happens when blood clots form in deep veins, usually in the legs. The thick blood sticks together and creates dangerous blockages.
Blood clots can break free and travel to other parts of the body. When clots reach the lungs, they cause pulmonary embolism. This blocks blood flow to the lungs and can be life-threatening.
Signs of blood clots include:
- Swelling in legs or arms
- Pain or tenderness in affected areas
- Red or warm skin
- Sudden shortness of breath
People with consistently high hemoglobin levels face serious health risks[2] from these clots forming throughout their body.
Stroke and Strokes
High hemoglobin makes blood thick and hard to pump. This puts extra strain on blood vessels in the brain.
Blood clots from thick hemoglobin can travel to the brain and block blood flow. When brain cells don’t get oxygen, a stroke happens. Brain tissue starts dying within minutes.
Ischemic strokes are the most common type caused by high hemoglobin. These happen when clots block arteries leading to the brain.
The thick blood also damages small blood vessels over time. This makes future strokes more likely to happen.
Warning signs of stroke include:
- Sudden weakness on one side of the body
- Trouble speaking or understanding words
- Severe headache
- Vision problems
- Loss of balance
Heart Attacks and Heart Disease
The heart works harder to pump thick blood through the body. This extra work damages the heart muscle over time.
Blood clots from high hemoglobin can block arteries that feed the heart. When heart muscle doesn’t get oxygen, a heart attack happens. Heart tissue dies quickly without blood flow.
Coronary artery disease develops when thick blood damages arteries around the heart. These damaged arteries become narrow and blocked more easily.
High hemoglobin also raises blood pressure because the heart pumps harder. High blood pressure damages blood vessels and makes heart problems worse.
Heart attack symptoms include:
- Chest pain or pressure
- Pain in arms, neck, or jaw
- Shortness of breath
- Sweating
- Nausea
The combination of thick blood and extra heart work creates a dangerous cycle that leads to serious heart disease.
Primary and Secondary Causes of High Hemoglobin
High hemoglobin stems from two main categories: primary causes like polycythemia vera where bone marrow overproduces red blood cells, and secondary causes where the body responds to low oxygen or other medical conditions by making more hemoglobin.
Polycythemia Vera and Blood Cancer
Polycythemia vera is a rare blood cancer that causes bone marrow to make too many red blood cells. This condition happens when genes in blood-making cells change or mutate.
Unlike other causes of high hemoglobin, polycythemia vera occurs without any trigger from the body. The bone marrow simply produces excess red blood cells on its own.
Common symptoms include:
- Thick, sticky blood that moves slowly
- Increased risk of blood clots
- Enlarged spleen
- Itchy skin, especially after warm baths
Other blood cancers can also raise hemoglobin levels. These cancers affect how the body makes and controls blood cells.
People with polycythemia vera need ongoing medical care. Treatment often involves removing blood regularly to reduce red blood cell counts.
Secondary Polycythemia and Underlying Conditions
Secondary polycythemia develops when the body makes more red blood cells to cope with low oxygen levels or other medical problems. The kidneys release a hormone called erythropoietin that tells bone marrow to produce more red blood cells.
Lung diseases commonly cause secondary polycythemia:
- Chronic obstructive pulmonary disease (COPD)
- Emphysema
- Pulmonary fibrosis
- Sleep apnea
These conditions reduce oxygen in the blood. The body responds by making more hemoglobin to carry available oxygen better.
Heart problems like congenital heart disease can also trigger high hemoglobin. When the heart cannot pump blood effectively, organs receive less oxygen.
Kidney disease sometimes causes high hemoglobin levels. Diseased kidneys may produce too much erythropoietin, leading to excess red blood cell production.
Other medical causes include:
- Tumors that make erythropoietin
- Certain medications like testosterone
- Blood disorders affecting oxygen transport
Lifestyle and Environmental Factors
Several lifestyle choices and environmental conditions can raise hemoglobin levels temporarily or permanently.
Smoking significantly increases hemoglobin because it reduces oxygen in the blood. Carbon monoxide from cigarettes binds to hemoglobin better than oxygen does. The body compensates by making more red blood cells.
Performance-enhancing substances affect hemoglobin:
- Anabolic steroids boost red blood cell production
- Testosterone therapy can raise hemoglobin levels
- Some athletes misuse these substances illegally
High altitude living naturally increases hemoglobin levels. At elevations above 8,000 feet, the air contains less oxygen. People who live at high altitudes may have higher normal hemoglobin levels[4] as their bodies adapt.
Dehydration can make hemoglobin appear high on blood tests. When the body loses water, blood becomes more concentrated. Proper hydration often returns levels to normal ranges.
Poor nutrition rarely causes high hemoglobin directly. However, certain dietary supplements containing iron or vitamins may contribute to elevated levels in some people.
Diagnosis: How High Hemoglobin Is Detected
Doctors use blood tests to find high hemoglobin levels, with a complete blood count being the main test. Additional tests may check oxygen levels and hormone levels to find the cause.
Hemoglobin Test and Complete Blood Count
A blood test is the only way to know if someone has high hemoglobin[1]. The complete blood count measures hemoglobin levels in the blood.
Normal hemoglobin levels vary by age and sex:
| Group | High Hemoglobin Level |
|---|---|
| Adult men | Above 16.5 g/dL |
| Adult women | Above 16 g/dL |
| Children | Above 16.6 g/dL |
| Infants | Above 18 g/dL |
The hemoglobin test also shows the red blood cell count. People with high hemoglobin often have too many red blood cells.
Doctors may find high hemoglobin when testing for other health problems. The complete blood count gives a full picture of all blood cells, not just hemoglobin.
Further Blood Tests and Oxygen Levels
Doctors order more tests when hemoglobin levels are high. They check erythropoietin levels, which is a hormone that tells the body to make red blood cells.
Blood oxygen tests show how well oxygen moves through the body. Low oxygen levels can cause the body to make more hemoglobin and red blood cells.
Other tests look for diseases that might cause high hemoglobin. These include kidney problems, heart disease, and lung conditions that affect oxygen delivery.
Doctors also check if medications or lifestyle factors cause the high levels. Living at high altitudes can naturally raise hemoglobin because there is less oxygen in the air.
Treatment Options and Prevention Strategies
Doctors use several methods to lower high hemoglobin levels, including removing blood through phlebotomy, prescribing medications, and recommending lifestyle changes. The right treatment depends on what caused the high levels and how severe they are.
Phlebotomy and Blood Donation
Therapeutic phlebotomy is the most common treatment for high hemoglobin levels. This procedure removes blood from the body to reduce the number of red blood cells.
During phlebotomy, doctors remove one to two units of blood at a time. Most patients need treatments every few weeks until their levels return to normal.
Regular blood donation can help some people maintain healthy hemoglobin levels. However, patients should talk to their doctor before donating blood as a treatment method.
Benefits of phlebotomy include:
- Quick reduction in hemoglobin levels
- Lower risk of blood clots
- Improved blood flow
- Reduced symptoms like headaches
The procedure takes about 30 minutes and is similar to donating blood. Patients may feel tired after treatment but can usually return to normal activities the same day.
Medications and Aspirin Use
Doctors may prescribe low-dose aspirin to reduce the risk of blood clots in patients with high hemoglobin. Aspirin helps prevent platelets from sticking together.
The typical dose is 81 mg daily, also called baby aspirin. Patients should never start aspirin therapy without medical supervision.
Other medications target the underlying cause of high hemoglobin. For example, doctors may prescribe drugs to treat heart or lung conditions that contribute to elevated levels.
Common medication approaches:
- Low-dose aspirin for clot prevention
- Medications for underlying conditions
- Drugs to suppress blood cell production
Some patients may need stronger blood-thinning medications if aspirin is not enough. Regular blood tests help doctors monitor treatment effectiveness.
Lifestyle Changes and Physical Activity
Quitting smoking is one of the most important steps for lowering hemoglobin levels. Smoking reduces oxygen in the blood, causing the body to make more red blood cells.
Most people see improvements in hemoglobin levels within weeks of quitting smoking. The body gradually adjusts to having more oxygen available.
Regular physical activity helps improve circulation and oxygen delivery throughout the body. Exercise also supports weight loss, which can help reduce hemoglobin levels.
Effective lifestyle changes include:
- Quit smoking completely
- Exercise 30 minutes daily
- Maintain a healthy weight
- Avoid secondhand smoke
Weight loss can be particularly helpful for people whose high hemoglobin relates to sleep problems or breathing issues. Even modest weight reduction can make a difference.
Diet and Hydration Management
Staying well-hydrated helps thin the blood and reduce hemoglobin concentration. Patients should drink plenty of water throughout the day.
People with high hemoglobin may need to limit iron-rich foods. Too much iron can contribute to higher red blood cell production.
Foods to limit:
- Red meat
- Organ meats
- Iron-fortified cereals
- Spinach and dark leafy greens
Proper nutrition focuses on balanced meals without excess iron. Patients should work with a dietitian to create an appropriate meal plan.
Some people benefit from eating foods that interfere with iron absorption, such as dairy products or foods high in calcium. However, dietary changes should complement medical treatment, not replace it.
Frequently Asked Questions
High hemoglobin levels can cause various symptoms and health risks that patients often have questions about. Understanding the warning signs, causes, and when to seek emergency care helps people make informed decisions about their health.
What are the potential symptoms associated with elevated hemoglobin levels?
High hemoglobin can cause several noticeable symptoms[1] that affect daily life. Patients often experience dizziness and headaches as common early signs.
Fatigue occurs even with normal activity levels. The body works harder to pump thicker blood through vessels.
Easy bruising or bleeding happens more frequently. Small cuts may bleed longer than usual.
Excessive sweating[1] can occur without physical activity. Joint swelling may develop in hands, feet, or other areas.
Unexplained weight loss sometimes accompanies high hemoglobin. Yellowish eyes or skin[1] may appear as jaundice develops.
What could be the underlying causes of a high hemoglobin count?
Several factors can lead to elevated hemoglobin levels. Smoking reduces oxygen in the blood, causing the body to make more red blood cells.
Dehydration concentrates the blood and raises hemoglobin readings. Heart problems can trigger increased red blood cell production.
Living at high altitudes[4] causes the body to produce more hemoglobin. Lower oxygen levels at elevation prompt this natural response.
Certain medications and supplements can raise levels. Kidney disease may cause excess red blood cell production.
Bone marrow disorders sometimes create too many red blood cells. Lung diseases that reduce oxygen can trigger higher hemoglobin.
What steps should be taken when diagnosed with an abnormally high hemoglobin level?
Patients should work with their doctor to find the underlying cause. Blood tests help determine if the elevation is temporary or ongoing.
Quitting smoking[5] can help reduce hemoglobin levels naturally. Staying properly hydrated prevents concentration of blood cells.
Doctors may recommend avoiding iron supplements. Dietary changes[5] might include reducing iron-rich foods.
Regular monitoring through blood tests tracks progress. Some patients need medications to reduce red blood cell production.
Therapeutic phlebotomy removes excess blood in severe cases. This procedure lowers hemoglobin levels quickly when needed.
What risks are involved when dealing with increased levels of hemoglobin?
High hemoglobin levels can lead to serious blood clots[1]. Thicker blood moves more slowly through vessels.
Blood clots can form in legs, lungs, or brain. These clots may cause strokes, heart attacks, or pulmonary embolisms.
High blood pressure[5] may develop as the heart works harder. Circulation problems affect organs throughout the body.
Vision problems can occur from blood vessel changes in the eyes. Kidney damage may result from poor blood flow.
Heart strain increases the risk of heart failure. Early treatment reduces these serious complications.
At what point does a high hemoglobin measurement become a medical emergency?
Emergency care is needed when symptoms become severe or sudden. Chest pain, trouble breathing, or severe headaches require immediate attention.
Sudden weakness on one side of the body suggests a stroke. Vision changes or speech problems need urgent evaluation.
Severe leg pain with swelling may indicate blood clots. Coughing up blood requires emergency treatment.
Hemoglobin levels above 18-20 g/dL[1] often need immediate medical intervention. Very high levels increase clot risk significantly.
Any combination of multiple symptoms warrants emergency evaluation. Quick treatment prevents life-threatening complications.
Can an elevated hemoglobin level indicate the presence of an underlying cancer?
Yes, some cancers can cause high hemoglobin levels. Kidney cancer sometimes produces excess hormones that stimulate red blood cell production.
Liver cancer may affect blood cell regulation. Certain blood cancers directly increase red blood cell counts.
Lung cancer can reduce oxygen levels, triggering higher hemoglobin production. Brain tumors affecting hormone centers may cause elevation.
However, most high hemoglobin cases are not cancer-related. Common causes include smoking, dehydration, and heart conditions.
Doctors use additional tests to rule out cancer when needed. Blood work, imaging, and physical exams help make accurate diagnoses.
References
- High Hemoglobin Count: Causes, Testing & Treatment. https://my.clevelandclinic.org/health/symptoms/17789-high-hemoglobin-count Accessed November 9, 2025
- High Haemoglobin Levels: Here’s What It Could Mean for Your Body. https://www.onlymyhealth.com/what-happens-to-your-body-when-haemoglobin-is-high-12977819049 Accessed November 9, 2025
- High hemoglobin levels can cause headaches. https://www.verywellhealth.com/high-hemoglobin-5211560 Accessed November 9, 2025
- High Hemoglobin Levels: Causes, Implications, and Next Steps. https://www.rupahealth.com/post/high-hemoglobin-levels-causes-implications-and-next-steps Accessed November 9, 2025
- 403 Forbidden. https://www.apollohospitals.com/diseases-and-conditions/high-hemoglobin-count Accessed November 9, 2025
