What Causes Elevated Red Blood Cells?

Your blood carries oxygen throughout your body in red blood cells. When your red blood cell count is too high, your blood becomes thicker and flows less easily. This condition, called erythrocytosis or polycythemia, can result from your body making too many red blood cells, from losing plasma so the cells become more concentrated, or from an underlying medical problem that forces your bone marrow to overproduce them.

What Does It Mean to Have Elevated Red Blood Cells?

Your red blood cell count is measured as part of a complete blood count (CBC). For most adults, a normal range is roughly 4.35 to 5.65 million cells per microliter for men and 3.92 to 5.13 million for women, though exact numbers vary by lab. A result above these ranges is considered elevated.

Having a high red blood cell count is not a disease itself. It is a sign that something else is going on in your body. The cause may be temporary and harmless, like dehydration, or it may be a chronic condition that needs medical attention. The key is figuring out why your body has too many red blood cells.

Doctors often repeat the test to confirm the result before investigating further. A single high reading can be due to lab error, recent exercise, or not drinking enough water. If the elevation persists, then the search for an underlying cause begins.

What Are the Main Causes of Elevated Red Blood Cells?

The causes fall into three broad categories: primary, secondary, and relative polycythemia. Each has a different mechanism and different implications for your health.

Primary polycythemia — most often called polycythemia vera — is a bone marrow disorder. A genetic mutation (usually in the JAK2 gene) causes the marrow to produce too many red blood cells regardless of the body’s oxygen needs. This is a myeloproliferative neoplasm, a type of blood cancer that tends to be slow-growing. It is rare, affecting about 1 in 100,000 people each year.

Secondary polycythemia happens when something outside the bone marrow triggers increased red blood cell production. The most common trigger is chronic low oxygen (hypoxia). When your tissues sense low oxygen, the kidneys release erythropoietin (EPO), a hormone that tells the bone marrow to make more red blood cells. Conditions that cause chronic low oxygen include:

• Chronic obstructive pulmonary disease (COPD)
• Sleep apnea (repeated pauses in breathing during sleep)
• Heart failure or congenital heart disease
• Living at high altitude (above 8,000 feet)
• Heavy smoking (carbon monoxide in smoke binds to hemoglobin and reduces oxygen delivery)

Other secondary causes are not related to low oxygen. Certain kidney tumors or cysts can produce excess EPO on their own. Liver tumors, some adrenal tumors, and uterine fibroids can also raise EPO levels. Some athletes misuse EPO or blood transfusions (blood doping) to boost performance, which artificially raises the red blood cell count.

Relative polycythemia is not a true increase in red blood cells. Instead, the plasma (liquid part of your blood) decreases, making the cells more concentrated. Dehydration is the most common cause. Severe diarrhea, vomiting, excessive sweating, or not drinking enough fluids can reduce plasma volume. This raises the red blood cell count on the lab test, but the total number of cells is normal. Once you rehydrate, the count returns to baseline.

How Does the Body Normally Regulate Red Blood Cell Count?

Your body maintains a precise balance between producing and destroying red blood cells. The hormone erythropoietin (EPO) controls this balance. When oxygen levels in your blood are normal, the kidneys release a steady, low amount of EPO. If oxygen drops, EPO production increases, and the bone marrow ramps up red blood cell production.

Red blood cells live about 120 days. Old cells are broken down in the spleen and liver, and iron is recycled. Under healthy conditions, production equals destruction. Any disruption to this feedback loop — whether from low oxygen, EPO overproduction, or a bone marrow mutation — can push the count above normal.

One non‑obvious point: your body does not directly sense the number of red blood cells. It senses oxygen delivery. If blood is thick and slow, oxygen delivery may still be low enough to keep EPO high, creating a vicious cycle. That is one reason a high red blood cell count can sometimes cause more harm than benefit.

What Symptoms Are Linked to High Red Blood Cell Count?

Many people with mildly elevated red blood cells have no symptoms at all. The condition is discovered during routine blood work. When symptoms do appear, they are related to thicker blood and reduced blood flow.

Common symptoms include:

• Headaches, especially after lying down
• Dizziness or vertigo
• Blurred or double vision
• Fatigue and weakness
• Shortness of breath, especially with exertion
• Itching, often after a warm bath or shower (aquagenic pruritus)
• Reddish or purplish skin, particularly on the face, hands, and feet
• Ringing in the ears (tinnitus)
• Numbness or tingling in the hands and feet

In more advanced cases, thick blood can cause blood clots, stroke, heart attack, or pulmonary embolism. This is the main danger of untreated polycythemia vera and, to a lesser degree, of severe secondary polycythemia.

When Should You See a Doctor About Elevated Red Blood Cells?

If a routine blood test shows elevated red blood cells, your doctor will likely repeat the test to confirm. You do not need to panic. Many causes are manageable. However, you should see a doctor if:

• Your red blood cell count is persistently high on two or more tests.
• You have symptoms like headaches, vision changes, or itching.
• You have unexplained blood clots or a family history of blood disorders.
• You smoke heavily or have known lung, heart, or kidney disease.

Because a high red blood cell count can increase your risk of blood clots, it is worth investigating even if you feel fine. A primary care doctor can start the workup and refer you to a hematologist if needed.

How Is Elevated Red Blood Cell Count Diagnosed?

The diagnosis starts with a complete blood count (CBC). If your hemoglobin, hematocrit, or red blood cell count is high, the doctor will look for causes. The next step is often checking your oxygen saturation with a pulse oximeter. Low oxygen points toward secondary polycythemia from lung or heart disease.

Other tests may include:

• Erythropoietin (EPO) level — low in polycythemia vera, normal to high in secondary causes
• JAK2 gene mutation test — positive in most cases of polycythemia vera
• Arterial blood gas — to measure oxygen levels more precisely
• Imaging of kidneys, liver, or heart if a tumor or structural problem is suspected
• Sleep study if sleep apnea is likely

Distinguishing primary from secondary polycythemia guides treatment. Polycythemia vera may require phlebotomy (blood removal) or medication. Secondary polycythemia is treated by addressing the underlying cause — for example, CPAP for sleep apnea, quitting smoking, or surgery for a tumor.

What Treatments Are Available for High Red Blood Cell Count?

Treatment depends entirely on the cause. For relative polycythemia from dehydration, drinking enough fluids resolves the issue. No further treatment is needed.

For secondary polycythemia, the goal is to fix the oxygen problem or remove the EPO source. Examples:

• If you have sleep apnea, continuous positive airway pressure (CPAP) often lowers red blood cell counts.
• If you smoke, quitting usually brings the count back to normal over weeks to months.
• If you live at high altitude, moving to a lower elevation can help.
• If a kidney or liver tumor is producing EPO, surgical removal may cure the polycythemia.

For polycythemia vera, treatment focuses on reducing blood thickness and preventing clots. The mainstay is therapeutic phlebotomy — removing a pint of blood at regular intervals to lower the hematocrit below 45%. Some patients also need hydroxyurea or interferon to suppress bone marrow production. Low‑dose aspirin is often prescribed to reduce clot risk.

No clinical guidelines currently recommend specific dietary supplements or herbal remedies for lowering red blood cell counts. Some marketing claims suggest that fish oil or garlic can thin the blood, but these have not been proven to safely reduce red blood cell counts in controlled trials. Always talk to your doctor before taking any supplement, especially if you already have a high count.