What Happens If You Have Too Many Red Blood Cells?

Having too many red blood cells is a condition called erythrocytosis, or polycythemia. It means your bone marrow is producing more red blood cells than your body needs. This thickens your blood, which can slow blood flow and raise your risk of blood clots, stroke, or heart attack. The condition is treatable, and the right treatment depends on what is causing it.

What Does a High Red Blood Cell Count Mean for Your Body?

Red blood cells carry oxygen from your lungs to every tissue in your body. They also carry carbon dioxide back to your lungs. A normal red blood cell count keeps this system running smoothly.

When you have too many, your blood becomes thicker and more viscous. Thicker blood does not move through your small blood vessels as easily. This forces your heart to work harder to push blood through your circulatory system. It also increases the chance that clots will form inside your veins and arteries.

A blood clot can block a vessel and cut off blood supply to an organ. If that happens in the brain, it causes a stroke. If it happens in the heart, it causes a heart attack. Clots in the lungs, called pulmonary embolisms, are also a serious risk.

Not everyone with a high red blood cell count develops complications. But the risk goes up as the count climbs higher.

What Causes Too Many Red Blood Cells?

There are three main categories of causes. Each one works differently.

Primary erythrocytosis means the bone marrow itself is producing too many red blood cells on its own. The most common form is polycythemia vera, a bone marrow disease. In polycythemia vera, a genetic mutation causes the marrow to overproduce red blood cells regardless of what the body needs. This is a chronic condition that requires ongoing management.

Secondary erythrocytosis happens when something outside the bone marrow tells it to make more red blood cells. The most common trigger is low oxygen levels in the blood. Your kidneys detect low oxygen and release a hormone called erythropoietin, which signals the bone marrow to produce more red blood cells.

Conditions that cause low oxygen include chronic lung disease, sleep apnea, heart disease, and smoking. Living at high altitude also lowers blood oxygen, which is why people who live in mountain regions often have higher red blood cell counts. That is a normal adaptation, not a disease.

Relative erythrocytosis is different. Your actual number of red blood cells is normal, but your plasma volume is low. Plasma is the liquid part of your blood. When plasma drops, red blood cells become more concentrated. Dehydration is the most common cause. This is usually temporary and corrects when you restore fluids.

What Are the Symptoms of High Red Blood Cell Count?

Some people have no symptoms at all. The condition is often found during a routine blood test done for another reason.

When symptoms do appear, they come from the blood being too thick and from poor circulation. Common symptoms include:

• Headaches
• Dizziness
• Blurred vision
• Fatigue or weakness
• Shortness of breath
• Itchy skin, especially after a warm shower
• Ringing in the ears
• Numbness or tingling in the hands and feet

Some people notice a red or flushed appearance to their face. Others may experience high blood pressure.

One distinctive symptom of polycythemia vera is itching after bathing in warm water. This happens because the excess red blood cells release histamine when they break down. Not everyone with polycythemia vera has this symptom, but it is specific enough that doctors often ask about it.

Severe cases can cause more alarming symptoms like chest pain, confusion, or sudden weakness on one side of the body. These are signs of a blood clot and require emergency medical care.

How Is a High Red Blood Cell Count Diagnosed?

Diagnosis starts with a complete blood count, commonly called a CBC. This test measures your red blood cells, hemoglobin, and hematocrit.

Hemoglobin is the protein inside red blood cells that carries oxygen. Hematocrit is the percentage of your blood volume made up of red blood cells. Normal ranges vary slightly by age, sex, and laboratory, but generally a hematocrit above 48-50% in women and above 52-54% in men is considered elevated.

If your CBC shows high levels, your doctor will repeat the test to confirm. One high reading can happen from dehydration or a lab error. Two consistent readings are more meaningful.

Your doctor will also check your oxygen level. A pulse oximeter reading below normal suggests your body is responding to low oxygen. If your oxygen is normal, the cause is more likely in the bone marrow itself.

Further testing may include a blood test for erythropoietin levels and a test for the JAK2 mutation, which is present in most people with polycythemia vera. Imaging tests like an ultrasound of the kidneys or heart may be ordered if a secondary cause is suspected.

What Happens If You Have Too Many Red Blood Cells Left Untreated?

Untreated erythrocytosis carries real risks. The most serious is blood clotting. Studies consistently show that people with untreated polycythemia vera have a significantly higher risk of thrombosis, which is the medical term for a blood clot blocking a vessel.

Clots can cause stroke, heart attack, deep vein thrombosis, or pulmonary embolism. These are life-threatening events.

Another risk is bleeding. This may sound backwards, but very thick blood can actually damage platelets, which are the cells that help blood clot. Some people with polycythemia vera develop bleeding problems even though their red blood cell count is high.

Long-term, untreated polycythemia vera can also cause your spleen to enlarge. The spleen normally filters old red blood cells. When there are too many, the spleen works overtime and grows larger. An enlarged spleen can cause pain in the upper left abdomen and a feeling of fullness after eating very little.

In rare cases, polycythemia vera can progress to a more serious bone marrow condition. This is uncommon, but it is one reason why ongoing monitoring matters.

How Is High Red Blood Cell Count Treated?

Treatment depends entirely on the cause. There is no single approach that works for everyone.

For secondary erythrocytosis, the goal is to treat the underlying cause. If you have sleep apnea, treating it with CPAP may lower your red blood cell count. If you smoke, quitting can help. If a medication is the cause, your doctor may adjust it. For people with chronic lung disease, better oxygen management may be the answer.

For relative erythrocytosis, rehydration is usually enough. Drinking fluids restores plasma volume, and the red blood cell concentration returns to normal.

For polycythemia vera, the standard treatment is phlebotomy. This is the same process as donating blood. A healthcare provider removes a unit of blood from your vein, which lowers your red blood cell count and thins your blood. This is done on a schedule until your hematocrit reaches a target range, then repeated as needed to maintain it.

Some people also take medication to suppress bone marrow production. Drugs like hydroxyurea are used when phlebotomy alone is not enough or when a person has a history of blood clots.

Low-dose aspirin is often prescribed for people with polycythemia vera. It helps prevent blood clots by making platelets less sticky. Your doctor will decide if aspirin is right for you based on your bleeding risk.

There is no cure for polycythemia vera, but it can be managed effectively. Most people with the condition live normal lives with regular monitoring and treatment.

Can You Prevent High Red Blood Cell Count?

You cannot prevent polycythemia vera. It is caused by a genetic mutation that happens on its own. There is no lifestyle change that stops it from developing.

You can reduce your risk of secondary erythrocytosis. Quitting smoking is the single most effective step. Smoking lowers blood oxygen, which drives your body to produce more red blood cells.

Managing chronic conditions like heart disease, lung disease, and sleep apnea can also help. If you have been diagnosed with any of these, following your treatment plan matters.

Staying well hydrated is simple and effective. It prevents relative erythrocytosis and keeps your blood from becoming unnecessarily concentrated.

If you live at high altitude, a higher red blood cell count is expected. Your body is adapting to lower oxygen. You do not need treatment unless you develop symptoms or other risk factors.

When Should You See a Doctor?

See a doctor if you have persistent symptoms like headaches, dizziness, fatigue, or blurred vision that do not go away. These are common symptoms of many conditions, but they deserve evaluation.

Seek emergency care immediately if you have signs of a blood clot. These include sudden chest pain, shortness of breath, weakness on one side of your body, difficulty speaking, or severe abdominal pain.

If a routine blood test shows an elevated red blood cell count, do not panic. One elevated reading is not a diagnosis. Your doctor will repeat the test and investigate the cause before recommending any treatment.

Many people with high red blood cell counts live completely normal lives. The key is finding out why your count is high and addressing it with your doctor.