Erythrocytosis: Symptoms, Causes, Types, Diagnosis, Treatment and When to Seek Emergency Care — What You Need to Know
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Quick Answer: Erythrocytosis (also called polycythemia) means you have a higher-than-normal concentration of red blood cells in your blood, shown by elevated hematocrit or hemoglobin levels — in adults, hematocrit above 50% or hemoglobin above 17.5 g/dL in men, and above 45% or 15.3 g/dL in women. Causes range from mild (dehydration, vomiting, diarrhea, diuretics) to serious (polycythemia vera, other blood disorders, lung or heart disease, kidney conditions, certain tumors, smoking and some drugs). Too many red blood cells can thicken your blood and raise the risk of life-threatening blood clots, heart attacks and strokes. Treatment — such as phlebotomy, low-dose aspirin or red-cell-lowering medications — eases symptoms and prevents complications.
TL;DR: Erythrocytosis at a Glance
Erythrocytosis is a higher-than-normal concentration of red blood cells in the blood, also commonly called polycythemia. It is a sign rather than a disease — levels may be high for many reasons, and some causes, like dehydration, are less concerning than others, like polycythemia vera, a serious blood disorder. Getting diagnosed and treated can prevent complications such as life-threatening blood clots.
Limitation statement: This article contains no prevalence, incidence or survival statistics; no figures are available for how common erythrocytosis is. No statistics have been invented.
Fact | Key point |
What it is | A higher-than-normal concentration of red blood cells (erythrocytes) in your blood; also called polycythemia |
Lab markers | High hematocrit and/or hemoglobin levels |
Key thresholds (adults) | Men: hematocrit >50% or hemoglobin >17.5 g/dL; women (non-pregnant): hematocrit >45% or hemoglobin >15.3 g/dL |
Main risk | Blood can become too thick, raising the risk of blood clots, heart attacks or strokes |
Two broad types | Absolute (too many red blood cells) vs relative (too little plasma) |
Serious cause to rule out | Polycythemia vera, a myeloproliferative neoplasm requiring lifelong treatment |
Treatments | Phlebotomy, low-dose aspirin, red-cell-lowering medications, treatment of the underlying cause |
Self-care | Stop smoking, maintain a healthy weight, manage high blood pressure, avoid high altitudes |
What Is Erythrocytosis?
Erythrocytosis involves having a higher-than-normal concentration of red blood cells (erythrocytes) in your blood. Your blood consists of solid parts, including red blood cells, white blood cells and platelets. It also includes a liquid portion called plasma. Erythrocytosis describes having too many red blood cells (a solid part) in relation to plasma (the liquid part).
Erythrocytosis causes you to have high levels of hematocrit and/or hemoglobin. Hematocrit is the number of red blood cells you have. Hemoglobin is an essential protein found in red blood cells.
Erythrocytosis is also commonly called polycythemia.
What lab levels are associated with erythrocytosis?
Many factors can influence what's considered a normal concentration for red blood cells. Your age, sex and even the altitude where you live all play a role. Erythrocytosis is associated with elevated hematocrit and/or hemoglobin levels in adults. Your provider can measure these levels during a blood test.
Group | Hematocrit (HCT) | Hemoglobin (HB) |
Men | >50% | >17.5 g/dL |
Women (non-pregnant) | >45% | >15.3 g/dL |
How does erythrocytosis affect your body?
Red blood cells are important because they transport oxygen throughout your body. They keep your tissues oxygenated, nourished and healthy.
Too many red blood cells can impact your body in a variety of ways depending on what's causing your erythrocytosis. Some effects are mild while others are more serious. Many people only experience unpleasant symptoms, like headache or fatigue. More serious causes can cause your blood to become too thick, putting you at risk of blood clots, heart attacks or strokes.
It's important to work with your provider to determine what's causing your erythrocytosis so you receive the right treatment to provide symptom relief or prevent complications, as needed.
What Are the Types of Erythrocytosis?
Erythrocytosis is classified based on the blood composition that causes the high concentration of red blood cells.
Type | Mechanism | Example |
Absolute erythrocytosis | You have more red blood cells than normal | Polycythemia vera, lung disease |
Relative erythrocytosis | You don't have enough plasma in relation to your red blood cells | Dehydration |
Absolute erythrocytosis involves a greater variety of causes than relative erythrocytosis. It's further broken down based on whether its causes are considered primary or secondary.
What is primary erythrocytosis?
Primary erythrocytosis results from problems in the spongy tissue inside of your bones called bone marrow. Bone marrow is the "primary" site in your body where red blood cells get made.
With primary erythrocytosis, red blood cell production increases in your bone marrow because of a genetic defect in the cells that eventually mature into red blood cells. These cells are called stem cells or progenitor cells. A genetic defect is an error in a cell's code that tells it how to behave. A genetic defect can cause a cell to multiply out of control, creating too many red blood cells.
You can develop a genetic mutation over time (acquired), or you may be born with a genetic disorder (inherited).
Primary subtype | Description |
Acquired primary erythrocytosis | The most common type is polycythemia vera — one of the most serious conditions associated with erythrocytosis. It's a specific type of erythrocytosis, not the same condition as erythrocytosis itself |
Inherited primary erythrocytosis | Gene mutations inherited from your parents cause your bone marrow to produce too many red blood cells |
What is secondary erythrocytosis?
Secondary erythrocytosis results from problems outside of your bone marrow. Most secondary erythrocytosis involves your body producing too much of a hormone called erythropoietin (EPO). Like all hormones, EPO is a chemical messenger. EPO tells your bone marrow to make more red blood cells.
For example, conditions that deprive your body of oxygen, like lung disease, trigger your body to produce more EPO. EPO tells your bone marrow to produce more red blood cells, which transport more oxygen to your body's tissues. With secondary erythrocytosis, the red blood cell production is too much.
Some genetic conditions can also cause secondary erythrocytosis. Unlike primary erythrocytosis, these mutations don't involve genetic mutations in your bone marrow.
What Are the Symptoms of Erythrocytosis?
Your symptoms (including how severe they are) will depend on what's causing your erythrocytosis.
Source category | Symptoms |
Secondary causes (typically milder) | Headaches, confusion, trouble sleeping, weakness and fatigue |
Primary causes (typically more severe) | High blood pressure, night sweats, unexplained weight loss, severe joint pain/swelling/tenderness (gout), bleeding problems (frequent nosebleeds, easy bruising), itchy skin (may feel worse after warm water), tingling (pins and needles) in arms, legs, hands or feet, burning and redness especially in face, hands or feet |
What causes relative erythrocytosis?
Not having enough fluids can cause relative erythrocytosis. Vomiting, diarrhea and medicines called diuretics can cause you to have too little liquid in your blood. A diuretic helps your kidneys move water out of your body. You may need diuretics if you have high blood pressure or if excess fluid has collected in your body.
What causes absolute (primary) erythrocytosis?
Primary erythrocytosis often results from a genetic mutation that affects your bone marrow. Causes include polycythemia vera and other myeloproliferative neoplasms (myeloproliferative disorders) — conditions that can cause too many blood cells, including red blood cells, to get made in your bone marrow. Polycythemia vera is the most common type of myeloproliferative disorder associated with erythrocytosis. Conditions involving inherited genetic mutations can also cause your marrow to make too many red blood cells.
What causes absolute (secondary) erythrocytosis?
Secondary erythrocytosis usually involves high levels of EPO. Causes include:
Conditions that deprive your tissues of oxygen: Lung disease, heart disease and sleep apnea can cause your body to have too little oxygen; EPO levels rise in response and more red blood cells are made. A group of conditions called hemoglobinopathy can also cause secondary erythrocytosis — these involve problems with hemoglobin, the essential protein that makes up red blood cells.
Kidney conditions and transplants: Conditions include renal artery stenosis and hydronephrosis. Erythrocytosis can also occur after a kidney transplant.
Tumors: Some tumors secrete excess EPO — cancerous tumors like renal cell carcinoma, hemangioblastoma, hepatocellular carcinoma and parathyroid carcinoma, and benign tumors like uterine fibroids, pheochromocytoma and meningioma.
Carbon monoxide poisoning and smoking: Carbon monoxide poisoning can deprive your tissues of oxygen. Excessive smoking can cause carbon monoxide poisoning.
Drugs and medications: Anabolic steroids and other performance-enhancing drugs used in sports can cause secondary erythrocytosis. Taking testosterone can also lead to erythrocytosis.
How Is Erythrocytosis Diagnosed?
Your healthcare provider may perform various tests and procedures to determine what's causing your high concentration of red blood cells. To start, they'll rule out relative erythrocytosis (too little plasma in your blood) by asking questions about your medical history, medicines you're taking, lifestyle and symptoms. They may also perform a physical exam.
The next step is to determine whether your erythrocytosis is primary or secondary. In addition to considering the information above, your provider may perform several tests.
Test | What it shows |
Complete blood count (CBC) | How many red blood cells you have, plus hemoglobin and hematocrit levels |
Peripheral blood smear (PBS) | Blood examined beneath a microscope for abnormal cells; unusual shapes or sizes may signal a myeloproliferative neoplasm like polycythemia vera |
Kidney and liver function tests | Signs of kidney disease or a tumor causing high EPO or red blood cells |
Pulse oximetry | Oxygen level in your blood via a finger sensor; shows whether erythrocytosis is likely related to heart or lung disease |
Erythropoietin (EPO) test | EPO levels help distinguish primary (low EPO) from secondary (high EPO) erythrocytosis |
Urinalysis | Red blood cells in your urine may signal kidney disease is causing your erythrocytosis |
Your provider may perform other tests, including imaging and a bone marrow biopsy, if they suspect a specific condition like polycythemia vera.
How Is Erythrocytosis Treated?
Most causes of erythrocytosis can't be cured. Instead, treatment can help ease symptoms. With more serious causes, your provider may provide treatments to prevent potential complications, like blood clots.
What is phlebotomy for erythrocytosis?
Phlebotomy is the most common treatment for polycythemia vera. Your healthcare provider will remove blood to eliminate excess red blood cells and reduce your overall blood volume. Secondary causes of erythrocytosis don't often require this treatment.
What medications treat erythrocytosis?
Your provider may recommend you take a low dosage of aspirin regularly if you're at high risk of developing blood clots. Your provider may also prescribe medicines that can lower your red blood cell count, including hydroxycarbamide, hydroxyurea, busulfan, interferon alfa and ruxolitinib.
Your provider may recommend specific medications and procedures to treat the underlying condition causing erythrocytosis.
Treatment | When it's used |
Phlebotomy (venesection) | Most common treatment for polycythemia vera — removes blood to eliminate excess red blood cells and reduce blood volume |
Low-dose aspirin | Taken regularly if you're at high risk of developing blood clots |
Hydroxycarbamide / hydroxyurea | Prescribed to lower your red blood cell count |
Busulfan | Prescribed to lower your red blood cell count |
Interferon alfa | Prescribed to lower your red blood cell count |
Ruxolitinib | Prescribed to lower your red blood cell count |
Treatment of the underlying condition | Specific medications and procedures for whatever is causing the erythrocytosis |
What can I expect if I have erythrocytosis?
Your experience depends on what's causing your erythrocytosis. Many inherited causes of primary erythrocytosis only cause mild symptoms and aren't life-threatening. More serious conditions, like polycythemia vera, require lifelong treatment.
When Should I Go to the ER?
EMERGENCY: It's a good idea to know the signs of a blood clot if you have a condition related to your erythrocytosis that puts you at risk. Get immediate medical attention (call 911 or go to the nearest emergency room) if you notice signs of deep vein thrombosis (DVT), pulmonary embolism, stroke or heart attack. Symptoms include: chest pain (heart attack/pulmonary embolism), shortness of breath (heart attack/pulmonary embolism), feeling lightheaded or dizzy (heart attack/pulmonary embolism), sudden loss of balance or coordination (stroke), muscle weakness or numbness in your body (stroke), and swelling, pain or redness in one leg (DVT).
Living With Erythrocytosis
How can I take care of myself?
Follow your provider's instructions based on your condition's causes and severity. In the meantime, specific lifestyle changes that can help include stopping smoking, maintaining a healthy body weight, managing high blood pressure and avoiding environments with high altitudes.
Self-care step | Why it helps |
Stop smoking | Removes a direct cause of carbon-monoxide-driven red cell increases |
Maintain a healthy body weight | Supports overall cardiovascular health |
Manage high blood pressure | Addresses a high blood-pressure risk factor |
Avoid high altitudes | High altitude lowers available oxygen, a red-cell trigger |
Clinical care-team note: "Erythrocytosis involves having a higher-than-normal concentration of red blood cells (erythrocytes) in your blood. Your healthcare provider will work with you to determine what's causing your high concentration of red blood cells. In some instances, simple lifestyle changes — like reducing or stopping a medication — may fix the issue. If a more serious condition is causing your erythrocytosis, your provider will monitor your condition closely to ensure you receive the treatment you need."
Conclusion: A Sign That Deserves a Thorough Workup
Erythrocytosis is not a single disease but a laboratory finding — too many red blood cells relative to plasma. Because its causes span the entire seriousness spectrum, from simple dehydration to the blood cancer polycythemia vera, the single most important step is a complete diagnostic workup: confirming the elevation on a CBC, ruling out relative (fluid-depletion) causes, and using the EPO level and other tests to separate primary from secondary erythrocytosis. Once the cause is known, treatment targets it — phlebotomy for polycythemia vera, low-dose aspirin and red-cell-lowering medications to prevent clots, and management of whatever underlying condition is driving the overproduction. Knowing the warning signs of blood clots, and acting on them immediately, is the safety net that makes the difference between a manageable condition and a life-threatening emergency.
Take these three steps:
1. Get the cause identified — elevated red cell counts warrant a CBC, EPO test and targeted workup, because treatment depends entirely on whether the cause is dehydration, a medication, lung or kidney disease, or a bone marrow disorder.
2. Follow the prescribed plan consistently — phlebotomy and medications such as low-dose aspirin work to keep blood from thickening; skipping them raises clot, stroke and heart attack risk.
3. Know your emergency signs — chest pain, shortness of breath, dizziness, sudden balance loss, one-sided weakness or a swollen painful leg mean immediate emergency care.
This article provides general information and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for diagnosis and treatment.
Frequently Asked Questions
What is erythrocytosis?
Erythrocytosis involves having a higher-than-normal concentration of red blood cells (erythrocytes) in your blood. Erythrocytosis is also commonly called polycythemia.
What does polycythemia mean?
Polycythemia is another name for erythrocytosis — a higher-than-normal concentration of red blood cells in your blood.
What is the difference between erythrocytosis and polycythemia vera?
Polycythemia vera is a specific type of erythrocytosis — the conditions aren't the same. Polycythemia vera is a myeloproliferative neoplasm and one of the most serious conditions associated with erythrocytosis.
What are hematocrit and hemoglobin?
Hematocrit is the number of red blood cells you have. Hemoglobin is an essential protein found in red blood cells.
What hematocrit and hemoglobin levels indicate erythrocytosis in men?
In men, a hematocrit above 50% or a hemoglobin above 17.5 g/dL.
What hematocrit and hemoglobin levels indicate erythrocytosis in women?
In women (non-pregnant), a hematocrit above 45% or a hemoglobin above 15.3 g/dL.
Is erythrocytosis a disease?
It's described as a finding — your levels may be high for many reasons. Some causes, like dehydration, are less concerning than others, like polycythemia vera, a serious blood disorder.
Is erythrocytosis dangerous?
More serious causes of erythrocytosis can cause your blood to become too thick, putting you at risk of blood clots, heart attacks or strokes. Getting diagnosed and treated can prevent these complications.
What are the types of erythrocytosis?
Absolute erythrocytosis (you have more red blood cells than normal) and relative erythrocytosis (you don't have enough plasma in relation to your red blood cells). Absolute erythrocytosis is further broken down into primary (bone marrow problem) and secondary (outside the bone marrow) causes.
What is relative erythrocytosis?
Relative erythrocytosis causes a high concentration of red blood cells because you don't have enough plasma in relation to the number of red blood cells. Dehydration may lead to too little liquid or plasma in your blood.
What is absolute erythrocytosis?
Absolute erythrocytosis causes a high concentration of red blood cells because you have more red blood cells than normal.
What is primary erythrocytosis?
Primary erythrocytosis results from problems in your bone marrow — red blood cell production increases because of a genetic defect in the stem or progenitor cells that mature into red blood cells.
What is secondary erythrocytosis?
Secondary erythrocytosis results from problems outside of your bone marrow, usually involving too much of the hormone erythropoietin (EPO), which tells your bone marrow to make more red blood cells.
Can dehydration cause erythrocytosis?
Yes. Not having enough fluids can cause relative erythrocytosis. Vomiting, diarrhea and diuretics can cause you to have too little liquid in your blood.
Can medications cause erythrocytosis?
Yes. Diuretics can cause relative erythrocytosis. Anabolic steroids, other performance-enhancing drugs and testosterone can cause secondary erythrocytosis.
Can smoking cause erythrocytosis?
Yes. Excessive smoking can cause carbon monoxide poisoning, which deprives your tissues of oxygen and can cause secondary erythrocytosis.
Can testosterone cause erythrocytosis?
Yes. Taking testosterone can lead to erythrocytosis.
Can sleep apnea cause erythrocytosis?
Yes. Conditions that deprive your tissues of oxygen — including lung disease, heart disease and sleep apnea — trigger higher EPO levels and more red blood cell production, causing secondary erythrocytosis.
Can kidney disease cause erythrocytosis?
Yes. Conditions like renal artery stenosis and hydronephrosis cause erythrocytosis, and it can also occur after a kidney transplant.
Can tumors cause erythrocytosis?
Yes. Some tumors secrete excess EPO, including cancerous tumors (renal cell carcinoma, hemangioblastoma, hepatocellular carcinoma, parathyroid carcinoma) and benign tumors (uterine fibroids, pheochromocytoma, meningioma).
What is erythropoietin (EPO) and how does it relate to erythrocytosis?
EPO is a hormone and chemical messenger that tells your bone marrow to make more red blood cells. Conditions that deprive your body of oxygen trigger more EPO production.
Is erythrocytosis inherited?
It can be. You can inherit gene mutations from your parents that cause your bone marrow to produce too many red blood cells, and some genetic conditions cause secondary erythrocytosis through mutations that don't involve the bone marrow.
Does altitude affect red blood cell levels?
Yes. The altitude where you live influences what's considered a normal concentration of red blood cells. Avoiding high altitudes is a recommended self-care step.
What are the symptoms of erythrocytosis?
Secondary causes may cause headaches, confusion, trouble sleeping, weakness and fatigue. Primary causes may cause more severe symptoms including high blood pressure, night sweats, unexplained weight loss, gout, bleeding problems, itchy skin, tingling in the limbs, and burning/redness in the face, hands or feet.
Can erythrocytosis cause itchy skin?
Yes. Itchy skin that may feel worse after warm water is listed among the symptoms of primary causes of erythrocytosis.
Can erythrocytosis cause nosebleeds?
Yes. Bleeding problems, including frequent nosebleeds and bruising easily, are among the symptoms of primary causes.
How is erythrocytosis diagnosed?
Your provider rules out relative erythrocytosis through history, medication review, lifestyle questions and a physical exam, then determines whether it is primary or secondary using tests like a CBC, peripheral blood smear, kidney and liver function tests, pulse oximetry, an EPO test, urinalysis, and possibly imaging or a bone marrow biopsy.
Does a low EPO level mean polycythemia vera?
EPO levels are low with primary erythrocytosis and high with secondary erythrocytosis — the EPO test helps your provider distinguish between them.
How is erythrocytosis treated?
Most causes can't be cured, so treatment eases symptoms and prevents complications like blood clots. Options include phlebotomy (the most common treatment for polycythemia vera), low-dose aspirin, and medications that lower your red blood cell count such as hydroxycarbamide, hydroxyurea, busulfan, interferon alfa and ruxolitinib, plus treatment of the underlying cause.
What is phlebotomy for erythrocytosis?
Phlebotomy (venesection) removes blood to eliminate excess red blood cells and reduce your overall blood volume. It's the most common treatment for polycythemia vera; secondary causes don't often require it.
What is the outlook for erythrocytosis?
Your experience depends on the cause. Many inherited causes of primary erythrocytosis only cause mild symptoms and aren't life-threatening. More serious conditions, like polycythemia vera, require lifelong treatment.
Can erythrocytosis be prevented?
Self-care steps that help include stopping smoking, maintaining a healthy body weight, managing high blood pressure and avoiding environments with high altitudes. In some instances, simple lifestyle changes — like reducing or stopping a medication — may fix the issue.
When should I seek emergency care for erythrocytosis?
Get immediate medical attention if you notice signs of deep vein thrombosis (swelling, pain or redness in one leg), pulmonary embolism or heart attack (chest pain, shortness of breath, lightheadedness or dizziness), or stroke (sudden loss of balance or coordination, muscle weakness or numbness).
Can erythrocytosis cause blood clots?
Yes — more serious causes can make your blood too thick, putting you at risk of blood clots, heart attacks or strokes.
Additional Resources
For further reading, these authoritative external references support the information above:
Content reviewed and produced following the Rinnit editorial framework. Last updated: September 28, 2026.
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