What is the most common cause of high hemoglobin? A comprehensive guide

September 25, 2025 •

4 min read

According to health experts, a high hemoglobin count is most often a compensatory reaction to long-term low blood oxygen levels, a state known as hypoxia. This article will answer the critical question, what is the most common cause of high hemoglobin? and explain the underlying reasons for this condition.

Quick Summary

Chronic low oxygen levels, or hypoxia, are the most frequent trigger for high hemoglobin as the body compensates by producing more oxygen-carrying red blood cells.

Key Points

The most common cause: A high hemoglobin level is most often a compensatory response to chronic hypoxia, or low oxygen levels, in the blood.
Common triggers: Lifestyle factors like smoking and living at high altitudes commonly induce this compensatory response.
Chronic conditions: Lung and heart diseases, such as COPD and sleep apnea, are also frequent medical causes of chronic hypoxia.
Dehydration's effect: Dehydration can temporarily concentrate blood, causing a falsely high hemoglobin reading that resolves with rehydration.
Polycythemia vera: A less common but serious cause is polycythemia vera, a bone marrow cancer that causes an overproduction of red blood cells.
Complications: Persistently high hemoglobin can lead to increased blood viscosity, raising the risk of blood clots, strokes, and heart attacks.
Seek medical advice: A doctor's evaluation is crucial to determine the specific cause and appropriate course of treatment for high hemoglobin.

The role of hemoglobin and chronic hypoxia

Hemoglobin is the protein in your red blood cells responsible for carrying oxygen from your lungs to the rest of your body. When your body's tissues and organs don't receive enough oxygen over a prolonged period, a condition known as chronic hypoxia, the body's natural response is to ramp up red blood cell and, consequently, hemoglobin production. This physiological mechanism is the root of many of the most common causes of high hemoglobin.

Lifestyle and environmental factors causing chronic hypoxia

Certain lifestyle choices and environmental conditions can directly lead to chronic hypoxia and elevated hemoglobin levels.

Smoking

Cigarette smoke contains carbon monoxide, which binds to hemoglobin much more readily than oxygen, displacing it and reducing the blood's oxygen-carrying capacity. To compensate for this chronic oxygen deprivation, the bone marrow increases the production of red blood cells and hemoglobin, leading to higher-than-normal counts, a form of secondary polycythemia.

Living at a high altitude

Individuals who live at high altitudes, where the air's oxygen pressure is lower, experience a natural and sustained state of hypoxia. In response, their bodies produce more red blood cells to maximize oxygen absorption and delivery to the tissues. This is a normal and necessary adaptation, but it results in a naturally higher baseline hemoglobin level compared to people living at sea level.

Underlying medical conditions leading to hypoxia

Beyond lifestyle and environmental factors, several medical conditions can impair oxygen delivery and trigger a compensatory increase in hemoglobin.

Chronic obstructive pulmonary disease (COPD)

This long-term lung disease blocks airflow and reduces the lungs' ability to get oxygen into the bloodstream. In severe cases, the persistent hypoxemia stimulates the kidneys to release erythropoietin (EPO), a hormone that signals the bone marrow to produce more red blood cells.

Heart conditions

Congenital heart disease and heart failure can impede the heart's ability to pump blood effectively, leading to poor oxygen circulation. The body's response is to increase hemoglobin production to enhance the oxygen-carrying capacity of the compromised blood flow.

Obstructive sleep apnea

This common sleep disorder causes repeated interruptions in breathing during sleep. The resulting episodes of low blood oxygen levels overnight can signal the body to increase hemoglobin production to compensate for the chronic intermittent hypoxia.

Dehydration: A temporary and non-hypoxic cause

While not related to chronic hypoxia, dehydration is a very common cause of an artificially high hemoglobin count. When the body is dehydrated, the plasma volume (the fluid part of the blood) decreases. This concentrates the existing red blood cells, causing hemoglobin levels to appear elevated during a blood test. This is often called relative polycythemia, and the levels return to normal once the person is properly rehydrated.

Polycythemia vera: A primary bone marrow disorder

In a smaller number of cases, high hemoglobin is caused by a primary bone marrow disorder called polycythemia vera (PV). PV is a type of blood cancer where the bone marrow, for reasons unrelated to oxygen levels, overproduces red blood cells. This can lead to a dangerously high red blood cell count, thickening the blood and increasing the risk of blood clots, strokes, and other cardiovascular events. This is a different mechanism than the compensatory hypoxia response seen in most other cases.

Comparing common and less common causes


Feature	Common Causes (Hypoxia-related)	Less Common Cause (Polycythemia Vera)
Mechanism	Compensatory response to long-term oxygen deprivation.	Primary disorder where bone marrow overproduces red cells regardless of oxygen levels.
Triggers	Smoking, high altitude, chronic lung/heart conditions, sleep apnea.	Genetic mutation in the JAK2 gene.
Onset	Gradual, over months or years.	Slow onset, often over many years and discovered incidentally.
Reversibility	Often reversible by treating the underlying cause (e.g., quitting smoking, oxygen therapy).	Chronic, incurable condition managed with ongoing treatment.
Severity	Depends on the severity of the underlying condition.	Can lead to serious complications like blood clots, requiring careful management.

Symptoms and associated complications

Symptoms of high hemoglobin may include dizziness, fatigue, headaches, blurred vision, or an itchy sensation, especially after a warm bath. High hemoglobin increases blood viscosity, raising the risk of complications such as blood clots, stroke, and heart attack. The management of this condition therefore focuses on treating the underlying cause and reducing the risk of these serious complications.

Diagnosis and treatment

Diagnosis of high hemoglobin typically begins with a routine blood test called a complete blood count (CBC). If the hemoglobin level is high, a doctor will conduct further tests and review the patient's full medical history and lifestyle to determine the cause.

Treatment varies depending on the root cause. For lifestyle-related causes like smoking or living at high altitude, lifestyle changes can be highly effective. For chronic medical conditions, treating the underlying disease is the primary focus. In cases of polycythemia vera, therapeutic phlebotomy (removing blood) is often used to lower the red blood cell count.

Conclusion

While a variety of factors can lead to elevated hemoglobin, the most common reason is the body's adaptive response to a long-term lack of oxygen. This can result from lifestyle choices like smoking or living at high altitude, as well as chronic medical conditions affecting the heart or lungs. Dehydration can cause a temporary concentration of hemoglobin, and in rare cases, a bone marrow cancer like polycythemia vera is the cause. Consulting a healthcare professional for a proper diagnosis is the first and most important step to identify the cause and receive the correct treatment plan.

For more in-depth medical information on blood conditions, you can visit the Mayo Clinic's website.

Frequently Asked Questions

High hemoglobin doesn't always cause symptoms, but some people may experience dizziness, fatigue, or headaches. A very high count could also lead to a reddened complexion or a feeling of itchiness, especially after a warm bath or shower.

You should start by consulting your primary care physician, who can perform an initial blood test (CBC) and assessment. If a serious underlying condition is suspected, they may refer you to a hematologist, a specialist in blood disorders.

A diagnosis begins with a complete blood count (CBC) test, which measures the level of hemoglobin along with other blood components. If the result is high, the doctor will follow up with additional tests to determine the specific cause, such as checking oxygen saturation or performing a bone marrow biopsy.

Diet does not typically cause high hemoglobin, which is often a result of chronic hypoxia or a bone marrow disorder. However, a doctor may advise dietary changes to manage an underlying condition, such as heart or kidney disease, that contributes to the high levels.

Treatment depends entirely on the cause. It can range from lifestyle modifications (quitting smoking, moving to a lower altitude) to treating underlying heart or lung disease. In cases of polycythemia vera, treatment may involve therapeutic phlebotomy (blood removal) or medication.

High hemoglobin can be serious if it leads to complications like blood clots, which increase the risk of heart attack and stroke. The severity depends on the underlying cause. A doctor's evaluation is necessary to determine the risk level and proper management.

High hemoglobin from living at altitude is a normal physiological adaptation to low oxygen levels and is a compensatory mechanism. Polycythemia vera, on the other hand, is a serious medical disorder involving the overproduction of red blood cells due to a bone marrow malfunction, regardless of oxygen availability.