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Blood health

Red Blood Cell Count

Also known as: Erythrocyte count, RBC test, Part of Complete Blood Count (CBC)

A red blood cell (RBC) count measures the number of circulating red blood cells, not their size or hemoglobin content . Red blood cells are vital for carrying oxygen from your lungs to the rest of your body and shuttling carbon dioxide back to your lungs for exhalation. Because oxygen delivery is essential for every tissue, abnormalities in RBC count can affect energy, organ function, and overall health.

The RBC count is almost always part of a complete blood count (CBC), one of the most commonly ordered lab tests. It provides important context when evaluating overall health, detecting anemia, and monitoring chronic medical conditions.

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Key takeaways

  • Sample required: Blood (typically taken from a vein in the arm)

  • Tests for: Helps evaluate overall health, anemia, blood loss, dehydration, bone marrow disorders, and conditions affecting red blood cell production.

  • Healthy range: 4.6 to 6.2 million cells per microliter (cells/µL) for men; 4.2 to 5.4 million cells/µL for women; ranges vary slightly by lab, age, and sex.

What can an RBC test tell you?

A red blood cell count test is typically included in annual checkups and pre-surgical evaluations, but your provider can also use it to:

  • Evaluate certain symptoms. Fatigue, weakness, shortness of breath, or pallor may prompt testing.

  • Monitor chronic conditions. Kidney disease, bone marrow disorders, and lung or heart disease may affect RBC counts.

  • Check treatment response. Used to follow people being treated for anemia, chemotherapy, or bone marrow suppression.

Note: An RBC test does not diagnose conditions on its own but provides data that helps guide next steps.

What is being tested?

Red blood cells (erythrocytes) are produced in your bone marrow and circulate for about 120 days before being recycled by the spleen and liver. They contain hemoglobin, which delivers oxygen to your tissues and helps carry carbon dioxide away. Too few red blood cells can impair oxygen delivery, while too many can make blood thicker and harder to pump.

Where is the RBC test typically included?

The RBC test is part of the complete blood count (CBC), which also measures:

  • Hemoglobin and hematocrit

  • White blood cell (WBC) count

  • Platelets

  • Mean corpuscular volume (MCV) levels, a measure of the average size of your RBCs

CBCs are common in preventive care, hospital admissions, and surgery prep.

RBC testing is included as part of lab testing through Hims. Discover how to improve or optimize your health with recommendations based on your results.

Who should get an RBC test?

There are no universal screening guidelines for healthy adults, but an RBC count is commonly included in:

  • Routine checkups: Often bundled in the CBC

  • Symptom evaluation: Fatigue, dizziness, rapid heartbeat, or pallor

  • Risk factor evaluation: For chronic kidney disease, nutritional deficiencies, lung disease, or heart conditions

  • Ongoing monitoring: For chemotherapy, chronic disease, or treatment of anemia

How Labs by Hims works

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    Review your lab results to understand which areas of your health may need attention.

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    Identify potential health risks or system imbalances before they become more serious.

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Not available in all 50 states. Eligibility and provider order required. Lab results alone are not intended to diagnose, treat, or cure any condition. A provider will reach out about critical results and plans include access to 24/7 provider messaging.

Images for illustrative purposes only.

Frequently asked questions

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What causes changes in RBC levels?

Red blood cell (RBC) levels can change for many reasons related to oxygen needs, nutrition, or bone marrow activity. High RBC counts may occur with dehydration (relative increase), living at high altitude, smoking, or chronic lung disease, all of which increase the body’s demand for oxygen. They can also result from bone marrow overproduction (polycythemia vera) or certain medications, such as androgens.

Low RBC counts are more common and can be caused by iron, vitamin B12, or folate deficiency, blood loss from injury, gastrointestinal bleeding, and chronic illnesses like kidney disease. Levels may also drop due to bone marrow suppression from chemotherapy or toxins, or from hemolysis, the premature destruction of red blood cells seen in conditions like sickle cell disease or some autoimmune disorders.

Is fasting required?

No. No special preparation is needed, but you should let your provider know about any medications you take.

How long do results take?

Results are usually available within 24 hours.

How often should I get tested?

An RBC test is often included in annual checkups or ordered when symptoms arise. Your provider may recommend more frequent testing if you have a chronic condition.

Does insurance cover it?

Yes. Because it’s part of the CBC, RBC count is generally covered when ordered by a healthcare provider. Insurance is not required for lab testing available through the Hims platform.

What’s the difference between RBC count and hemoglobin?

RBC count measures the number of red blood cells, while hemoglobin measures the oxygen-carrying protein inside those cells. Both are part of the CBC, and results are interpreted together.

What tests are related to this biomarker?

• Hemoglobin and hematocrit

• Iron studies (ferritin, transferrin, serum iron)

• Vitamin B12 and folate levels

• Reticulocyte count

• Kidney function tests (creatinine, BUN)

• White blood cell count and platelet count

The information provided here is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always talk to a qualified healthcare provider about your specific health concerns.

Related biomarkers

See all biomarkers

Hematocrit

Hematocrit is a test that measures the percentage of your blood that is made up of red blood cells, which carry oxygen throughout your body. Being in the healthy range means your blood cells are successfully transporting oxygen to your tissues to sustain bodily functions.

Learn more about Hematocrit

Hemoglobin

Hemoglobin is the protein inside your red blood cells that carries oxygen to your muscles and brain. Being in the healthy range means your blood cells have what they need to move oxygen to your tissues successfully.

Learn more about Hemoglobin

Mean Corpuscular Hemoglobin Concentration (MCHC)

Mean corpuscular hemoglobin concentration (MCHC) measures the average concentration of hemoglobin in your red blood cells, which reflects how effectively they carry oxygen. When MCHC is in the healthy range, it indicates that the body is likely not experiencing any red blood cell disorders or iron deficiency.

Learn more about Mean Corpuscular Hemoglobin Concentration (MCHC)

Mean Corpuscular Hemoglobin (MCH)

Mean corpuscular hemoglobin (MCH) measures the average amount of hemoglobin in each red blood cell, which shows how well your blood can carry oxygen. A healthy level means your blood has enough hemoglobin for proper oxygen transport.

Learn more about Mean Corpuscular Hemoglobin (MCH)

Mean Corpuscular Volume (MCV)

Mean corpuscular volume (MCV) measures the average volume of your red blood cells, which can help reveal early signs of nutrient deficiencies or other blood conditions.

Learn more about Mean Corpuscular Volume (MCV)

Mean Platelet Volume (MPV)

Mean platelet volume (MPV) measures the average volume of your blood platelets, which play an essential role in blood clotting. When your MPV is in the healthy range, it suggests that your platelet volume is normal.

Learn more about Mean Platelet Volume (MPV)

Platelet Count

Platelets are the blood cells that help your body form clots, stopping bleeding when needed. A healthy platelet count means your body generally supports normal blood clotting when necessary.

Learn more about Platelet Count

Red Cell Distribution Width (RDW)

Red cell distribution width (RDW) measures the variation in the size of your red blood cells, which can help detect early signs of anemia or other blood conditions. A healthy RDW suggests that your red blood cells are uniform and efficiently transporting oxygen throughout your body.

Learn more about Red Cell Distribution Width (RDW)

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Reviewed by Felix Gussone, MD

Published 11/19/2025