What is wrong when your red blood cell count is high?

September 25, 2025 •

4 min read

According to health experts, an elevated red blood cell count, or erythrocytosis, makes your blood thicker and can increase your risk for blood clots. If you've been asking "what is wrong when your red blood cell count is high," it's essential to understand the various potential causes, ranging from simple dehydration to more serious underlying conditions.

Quick Summary

An elevated red blood cell count, known as erythrocytosis, is not a disease itself but a sign of another condition that can cause the body to produce more red blood cells or increase their concentration in the blood, such as low oxygen levels, dehydration, or a bone marrow disorder like polycythemia vera.

Key Points

Erythrocytosis Defined: A high red blood cell count (erythrocytosis) can be caused by the body producing too many RBCs or a decrease in blood plasma volume, like in dehydration.
Low Oxygen Response: Secondary erythrocytosis is often triggered by low blood oxygen levels (hypoxia) due to conditions like lung disease, heart failure, or living at high altitudes.
Polycythemia Vera: A rare blood cancer called polycythemia vera (PV) is a primary cause, where the bone marrow overproduces blood cells due to a genetic mutation.
Symptoms: Common symptoms include fatigue, headaches, dizziness, shortness of breath, and an itchy skin, though some may be asymptomatic.
Blood Clot Risk: The primary danger of erythrocytosis is an increased risk of blood clots, which can lead to serious events like a stroke or heart attack.
Diagnosis is Key: High RBC counts are usually found in a routine CBC and require further investigation to determine the specific underlying cause.
Treatment Varies: Treatment depends on the cause, ranging from simple rehydration for relative erythrocytosis to phlebotomy or medication for polycythemia vera.

Understanding a High Red Blood Cell Count

Having a high red blood cell (RBC) count, also known as erythrocytosis or polycythemia, means that the number of oxygen-carrying cells in your blood is higher than normal. While it is not always a cause for alarm, as simple dehydration can temporarily increase the concentration of RBCs, it can also signal an underlying medical issue. Because a high RBC count can lead to complications such as blood clots, it's important to investigate the cause with a healthcare professional.

Causes of Erythrocytosis

The reasons behind an elevated RBC count can be complex and are often categorized into three types: absolute, relative, and secondary. Understanding these distinctions is key to determining the root cause of the issue.

Secondary Erythrocytosis

This is the most common cause of a high RBC count and occurs when the body produces more red blood cells in response to low oxygen levels (hypoxia). Conditions that can lead to this include:

Chronic Lung Disease: Conditions like Chronic Obstructive Pulmonary Disease (COPD), emphysema, and pulmonary fibrosis damage lung tissue and impair the body's ability to get enough oxygen, triggering increased red blood cell production.
Heart Conditions: Heart failure or congenital heart disease can cause poor circulation and low blood oxygen, prompting the bone marrow to create more RBCs.
Sleep Apnea: Repeatedly disrupted breathing during sleep can cause periods of low blood oxygen, leading to higher RBC production.
High Altitude Living: Individuals who live at high elevations often have higher RBC counts as their bodies adapt to the lower oxygen levels in the air.
Smoking: Carbon monoxide from cigarette smoke can reduce the blood's oxygen-carrying capacity, prompting the body to produce more RBCs to compensate.
Kidney Conditions: In rare cases, kidney tumors or issues after a kidney transplant can cause the kidneys to produce excess erythropoietin (EPO), a hormone that stimulates RBC production.

Primary Erythrocytosis

This type of erythrocytosis originates from a problem within the bone marrow itself, where red blood cells are produced. The most notable example is polycythemia vera (PV), a rare blood cancer.

Polycythemia Vera: A genetic mutation causes the bone marrow to overproduce red blood cells, as well as white blood cells and platelets. This leads to an overall thickening of the blood, significantly increasing the risk of dangerous blood clots, strokes, and heart attacks.

Relative Erythrocytosis

This is not a true increase in the number of red blood cells but rather an increase in their concentration due to a decrease in the liquid component of blood, known as plasma.

Dehydration: The most common cause. When you don't drink enough fluids, the plasma volume in your blood decreases, making the proportion of red blood cells appear higher in a blood test.
Certain Medications: Diuretics, or "water pills," can cause excess fluid loss, leading to a temporary high RBC count.

Associated Symptoms and Risks

While some people with a high RBC count may have no noticeable symptoms, others can experience a range of issues due to the thicker, slower-moving blood. Common symptoms include fatigue, headaches, dizziness, shortness of breath, and visual disturbances. Some individuals with polycythemia vera may also experience an intense itching, particularly after a warm bath or shower. The most significant risk associated with erythrocytosis is the formation of blood clots, which can lead to serious complications such as:

Heart attack
Stroke
Pulmonary embolism
Enlarged spleen

Comparison of Major Causes of Erythrocytosis


Feature	Secondary Erythrocytosis	Polycythemia Vera (Primary)	Relative Erythrocytosis
Root Cause	Response to low oxygen levels	Bone marrow genetic mutation	Dehydration or fluid loss
Key Trigger	Hypoxia from lung/heart disease, altitude, or smoking	Uncontrolled stem cell production	Reduced plasma volume
Blood Viscosity	Increased due to more RBCs	Significantly increased due to more RBCs, WBCs, platelets	Increased due to plasma loss
Associated Complications	Varies based on underlying disease	Blood clots, enlarged spleen, gout, potential for leukemia transformation	Generally benign, resolves with rehydration
Treatment Focus	Address underlying cause (e.g., oxygen therapy, medication)	Phlebotomy to remove blood, chemotherapy drugs	Rehydration

Diagnosis and Treatment

A high red blood cell count is typically discovered during a routine blood test, such as a complete blood count (CBC). If your results are high, your doctor will likely perform a thorough physical exam and order further tests to determine the cause. These may include a hemoglobin or hematocrit test, or for suspected polycythemia vera, a bone marrow biopsy.

Treatment depends entirely on the underlying cause. If dehydration is the culprit, simply increasing your fluid intake may be all that's needed. For conditions causing low oxygen levels, treatment focuses on managing the primary disease, such as quitting smoking or using oxygen therapy. In the case of polycythemia vera, treatment may involve a procedure called phlebotomy to remove excess blood, as well as medications to suppress blood cell production.

Seeking Medical Advice

It is crucial to consult your doctor if a blood test shows a high RBC count. They can provide an accurate diagnosis and create an appropriate treatment plan to manage the condition and prevent potential complications. You can find more information on blood disorders from reputable health organizations like the National Heart, Lung, and and Blood Institute [link: https://www.nhlbi.nih.gov/health-topics/blood-disorders].

In conclusion, a high red blood cell count is a sign that something is amiss in your body, whether it's a simple concentration issue due to dehydration or a more complex medical condition. A proper diagnosis from a healthcare provider is the only way to understand what is wrong and take the necessary steps to protect your health.

Frequently Asked Questions

The medical term for a high red blood cell count is erythrocytosis. In some specific cases, especially when the cause is a bone marrow disorder, it may be referred to as polycythemia.

Not always. It can be a temporary issue caused by dehydration. However, it can also be a sign of a serious underlying condition like a chronic lung or heart disease, or a rare blood cancer like polycythemia vera. A doctor should investigate the cause.

After an initial high reading on a complete blood count (CBC), a doctor will perform a physical exam and may order additional tests. These can include looking for low blood oxygen levels, checking hydration status, or conducting specialized tests like a bone marrow biopsy if a bone marrow disorder is suspected.

Yes. Severe dehydration can lead to a temporarily high red blood cell count. This is because the volume of blood plasma decreases, making the concentration of red blood cells appear higher. Rehydrating usually resolves this issue.

Symptoms vary but can include fatigue, headaches, dizziness, blurred vision, itchy skin (especially after a hot bath), shortness of breath, and joint pain. In more severe cases, it can cause nosebleeds or other bleeding problems.

Polycythemia vera is a rare blood cancer in which a genetic mutation causes the bone marrow to produce too many blood cells, particularly red blood cells. This condition makes the blood thicker, increasing the risk of dangerous blood clots.

Management depends on the cause. For mild cases, staying well-hydrated is key. If caused by smoking, quitting is essential. For more serious underlying conditions, managing those diseases and avoiding extreme heat can be helpful. Always follow your doctor's recommendations.