A complete blood count, or CBC, is one of the most common blood tests ordered by doctors. It measures several parts of your blood, including your red blood cells. If your results come back flagged as “high,” it means your red blood cell count is above the normal range for your age and sex. A high red blood cell count is generally defined as a measurement that exceeds the upper limit of the standard reference range, which typically falls around 5.8 million cells per microliter for men and 5.2 million for women. When your count is this high, it means your blood is thicker than normal, which can affect how easily it flows through your veins and arteries.
What Is Considered A High Red Blood Cell Count?
Doctors use specific numbers to define a high red blood cell count. These numbers come from the reference ranges established by the laboratory processing your blood sample. While slight variations exist between labs, the standard upper limits are generally consistent across medical guidelines.
- For men: A count above 5.8 million cells per microliter is considered high.
- For women: A count above 5.2 million cells per microliter is considered high.
- For children: Normal ranges vary significantly by age, so your pediatrician will interpret the results based on the child’s specific age.
Your doctor will also look at two other values on your CBC report: hemoglobin and hematocrit. Hemoglobin is the protein inside red blood cells that carries oxygen. Hematocrit measures the percentage of your blood that is made up of red blood cells. A high red blood cell count usually accompanies high hemoglobin and hematocrit levels because these three values rise together when your body produces too many red blood cells.
What Causes Your Body To Produce Too Many Red Blood Cells?
Your bone marrow produces red blood cells in response to a hormone called erythropoietin, or EPO. Your kidneys release EPO when they sense that your blood oxygen levels are low. Several conditions can trigger this process and lead to a high red blood cell count.
Living at high altitudes is one common cause. At higher elevations, the air contains less oxygen, so your body naturally produces more red blood cells to compensate. People who live in mountainous regions like Denver or the Andes often have higher baseline counts than people living at sea level. This is a normal, healthy adaptation, not a disease.
Smoking is another frequent cause. Carbon monoxide in cigarette smoke binds to hemoglobin more readily than oxygen does. This reduces the amount of oxygen delivered to your tissues, prompting your kidneys to release more EPO and stimulate red blood cell production.
Certain medical conditions also cause high red blood cell counts. Chronic lung diseases like COPD and sleep apnea reduce blood oxygen levels. Congenital heart defects can allow oxygen-poor blood to circulate through the body. These conditions all signal your kidneys that more red blood cells are needed, and your body responds accordingly.
Some medications can raise your red blood cell count as well. Testosterone therapy and anabolic steroids stimulate red blood cell production. Doctors also prescribe synthetic EPO to treat anemia caused by kidney disease, but athletes sometimes misuse it to enhance performance, which can dangerously thicken the blood.
When Is A High Red Blood Cell Count A Bone Marrow Disease?
Sometimes the cause is not an external trigger but a problem within the bone marrow itself. Polycythemia vera is a myeloproliferative neoplasm, a type of blood cancer where the bone marrow produces too many red blood cells regardless of oxygen levels.
Polycythemia vera is rare, affecting roughly 44 to 57 people per 100,000 in the United States. Most people diagnosed with it are over 60 years old. The condition often results from a mutation in the JAK2 gene, which plays a role in blood cell production.
Unlike secondary causes of high red blood cells, polycythemia vera typically causes elevated white blood cell and platelet counts as well. The condition also tends to cause more noticeable symptoms because blood becomes significantly thicker. These symptoms may include headaches, dizziness, blurred vision, fatigue, and itching, especially after a warm shower.
The distinction between secondary causes and polycythemia vera matters for treatment. Secondary high red blood cell counts usually resolve when the underlying cause is addressed, such as quitting smoking or treating sleep apnea. Polycythemia vera requires ongoing management to reduce blood thickness and prevent complications like blood clots.
What Symptoms Does A High Red Blood Cell Count Cause?
A mildly elevated red blood cell count often produces no symptoms at all. Many people discover their count is high only through routine blood work for an unrelated reason.
As the count climbs higher, symptoms begin to appear. The increased thickness of your blood, a condition called hyperviscosity, makes it harder for blood to flow through small vessels. This can cause a range of symptoms that develop gradually.
- Headaches and dizziness
- Blurred vision or seeing spots
- Fatigue and weakness
- Shortness of breath
- Itching, particularly after a warm shower or bath
- Ringing in the ears
- Reddish or purplish skin discoloration, especially on the face
- Numbness or tingling in the hands and feet
The most serious risk of a high red blood cell count is blood clots. Thicker blood flows more slowly and is more likely to clot inside veins and arteries. Clots can cause deep vein thrombosis, pulmonary embolism, heart attack, or stroke. This is why doctors take significantly elevated counts seriously, even when symptoms are mild.
How Is A High Red Blood Cell Count Treated?
Treatment depends entirely on the underlying cause. Your doctor will first repeat the blood test to confirm the elevation is persistent rather than a temporary fluctuation. Dehydration alone can artificially raise red blood cell counts because it reduces the liquid portion of your blood, concentrating the cells.
For secondary causes, treatment targets the root problem. If you smoke, quitting smoking will gradually lower your count. If you have sleep apnea, using a CPAP machine at night can restore normal oxygen levels during sleep. If a medication is responsible, your doctor may adjust the dose or switch to an alternative.
For polycythemia vera or severely elevated counts from any cause, doctors often use therapeutic phlebotomy. This procedure involves removing a unit of blood, similar to donating blood, to reduce the total number of red blood cells in circulation. The goal is to bring your hematocrit below 45 percent for men and 42 percent for women, levels associated with lower clot risk.
Some patients also receive medication to suppress bone marrow red blood cell production. Hydroxyurea is the most commonly used drug for this purpose. Low-dose aspirin may also be prescribed to reduce the risk of blood clots, though this decision depends on your individual bleeding risk.
Can Diet Or Lifestyle Changes Lower A High Red Blood Cell Count?
Dietary changes alone cannot treat a clinically high red blood cell count. No food has been proven to lower red blood cell production directly. Claims that specific supplements or diets can “thin the blood” or reduce red blood cell counts are not supported by clinical evidence.
Staying well hydrated is important, though it does not lower your actual red blood cell count. Drinking enough water ensures your blood plasma volume is adequate, which prevents an artificially elevated reading caused by dehydration. If you are already dehydrated, increasing fluid intake can bring your count back to its true baseline.
Regular exercise and maintaining a healthy weight support overall cardiovascular health. However, these habits do not directly reduce red blood cell production. If your count is high due to an underlying condition like sleep apnea, treating that condition is the effective approach, not general lifestyle changes.
Avoid iron supplements unless your doctor confirms you have an iron deficiency. Iron is a key component of hemoglobin, and taking it unnecessarily will not lower your red blood cell count. It could actually support further red blood cell production if your body is already making too many.
When Should You See A Doctor About A High Red Blood Cell Count?
You should not attempt to interpret your own blood test results in isolation. A single value outside the reference range does not automatically mean you have a disease. Laboratories set their ranges so that a small percentage of healthy people will fall outside them.
If your CBC shows a high red blood cell count, your doctor will likely repeat the test to confirm the finding. They will also review your complete blood count for other abnormalities, such as elevated white blood cells or platelets, which can provide clues about the underlying cause.
Seek medical attention promptly if you experience symptoms of a blood clot, such as sudden chest pain, shortness of breath, leg swelling or pain, or neurological symptoms like weakness on one side of your body or difficulty speaking. These symptoms require immediate emergency care regardless of your known blood counts.
For most people, an incidentally discovered high red blood cell count is not an emergency. It is a finding that warrants a conversation with your doctor to determine the cause and decide whether any treatment is necessary. Many causes are benign or easily managed once identified.
Frequently Asked Questions
What level of red blood cell count is dangerously high?
Any count significantly above the upper reference limit, such as over 6 million cells per microliter in men or 5.5 million in women, carries increased risk of blood clots. The danger depends on how fast the count rose and whether you have other risk factors for clotting.
Can dehydration cause a high red blood cell count?
Yes, dehydration can temporarily raise your red blood cell count because it reduces the fluid portion of your blood, making the cells more concentrated. Repeating the test after adequate fluid intake will show whether the elevation was real or just due to dehydration.
Is a high red blood cell count always serious?
No, a mildly elevated count from living at high altitude or smoking is common and not immediately dangerous. A persistently high count without an identifiable secondary cause may indicate polycythemia vera and requires evaluation by a hematologist.
Can a high red blood cell count return to normal on its own?
It can if the cause is temporary, such as dehydration or recovery from an illness. If the cause is chronic, like sleep apnea or polycythemia vera, the count will remain elevated until the underlying condition is treated.
