Red Blood Cell Count Normal Range and Causes

What an RBC Count Measures

A red blood cell count measures the number of red blood cells in your blood. They are made in the bone marrow, spongy tissue inside large bones.

An RBC evaluation is almost always ordered as one part of a complete blood count (CBC). Healthcare providers use this measurement to help diagnose red blood cell disorders, including anemia, which occurs when the body does not create enough healthy red blood cells. You can explore the broader panel in our CBC blood test guide.

Why a Provider Orders an RBC Count

A provider may order an RBC count as part of a CBC for several reasons:

• At a routine checkup.
• To monitor treatments that might affect blood cell counts, such as chemotherapy.
• To monitor conditions such as chronic kidney disease.
• If you have symptoms of a low or high count.

RBC Count Normal Range

Clinical laboratory reports do not use one universal numeric range for an RBC count. Reference intervals vary among individual laboratories, and expected values differ based on age and sex. Because ranges differ by lab, age, and sex, you should compare your result with the reference range printed directly on your laboratory report. If your number falls outside the printed boundaries, your provider will interpret that value within the context of your overall medical history, physical symptoms, and companion lab markers.

Low Red Blood Cell Count Causes

Symptoms of a low count may include shortness of breath, physical weakness or fatigue, headaches, dizziness, an irregular heartbeat (arrhythmia), and pale skin. Several distinct health conditions and factors can cause a low red blood cell count:

• Anemia, which develops when the body cannot manufacture enough healthy red blood cells.
• Blood loss from injury or other problems.
• Malnutrition, occurring when a person does not consume enough calories, vitamins, or minerals.
• Kidney failure.
• Leukemia (a type of blood cancer) and multiple myeloma (a cancer of the bone marrow).
• Alcohol use disorder.
• Pregnancy.

High Red Blood Cell Count Causes

Symptoms of a high red blood cell count may include headache, dizziness, or vision problems. Conditions and factors that may cause a high red blood cell count include:

• Dehydration.
• Heart disease.
• Lung diseases and scarring of lung tissue, frequently related to cigarette smoking.
• Sleep apnea, a disorder that causes you to repeatedly stop breathing during sleep. You can read more about this condition in our sleep apnea overview.
• Polycythemia vera, a bone marrow disease that causes the marrow to make too many red blood cells.
• Kidney cancer.
• Living at a high altitude.
• Misuse of athletic performance drugs, including anabolic steroids.

Getting the Blood Drawn

A healthcare professional collects a red blood cell count sample by taking blood from a vein in your arm with a small needle. The entire draw usually takes under five minutes. No special preparation is needed. The procedure carries very little physical risk. Some individuals experience slight pain or bruising where the needle went in, but most symptoms go away quickly.

Tests That Follow an Abnormal RBC Count

A healthcare provider interprets an abnormal RBC count by evaluating your medical history, symptoms, and accompanying blood markers together. If the count is low or high, more tests may be needed to make a diagnosis, which can include:

• A reticulocyte count (counts reticulocytes, immature developing red blood cells; checks if bone marrow is making the right amount).
• Iron tests (iron is essential for making red blood cells).
• A vitamin B test (B vitamins are important for making red blood cells and keeping the body healthy).

What to Do With Your Result

To learn how to interpret your overall panel, see our blood test results guide. Compare your values directly against the reference interval on your lab report, and bring your red blood cell count to your next doctor appointment to review next steps with your provider.

Where to Find CBC Test Kits