Red Blood Cell Count (RBC Count)

Your doctor may order an RBC count to measure the number of red blood cells in your blood and find out whether the level is too low or too high. Low red blood cell counts can point to anemia, which may cause fatigue, weakness, dizziness, or shortness of breath, while high counts can signal other health conditions. This test is often part of a complete blood count (CBC) and helps your care team diagnose a condition, monitor ongoing treatment, or check how well your body is responding to therapy.

Doctors may order an RBC count to diagnose or monitor conditions such as anemia (low red blood cells), polycythemia (high red blood cells), or to check for blood loss, bone marrow disorders, or kidney disease. It can also be part of routine health checks or before certain treatments.

In most cases, no special preparation is needed for an RBC count, and you can usually eat and drink normally before your appointment. Keep taking your medications as prescribed, but tell your doctor about any prescription drugs, over-the-counter medicines, vitamins, or herbal supplements you use, since some of these can affect your results. Being well hydrated can make the blood draw easier, so drink plenty of water beforehand, and consider wearing a shirt with sleeves that can be rolled up above your elbow.

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if it involves a blood draw from a vein, but this depends on your doctor’s instructions. Wear comfortable clothing and plan for a short visit to the lab.

During the test, a health care professional will draw a small sample of blood, usually from a vein on the inside of your elbow or the back of your hand. An elastic band will be wrapped around your upper arm to make the vein easier to see, and the site will be cleaned with an antiseptic wipe. You may feel a quick pinch or sting when the needle goes in, and collecting the sample typically takes only a few minutes. Afterward, a cotton pad or small bandage will be placed on the spot, and you can return to your normal activities right away.

A healthcare professional will take a small sample of blood from a vein in your arm using a needle. The process is quick and typically painless, though you might feel a slight pinch. The blood sample is then sent to a lab for analysis.

Your results show whether your red blood cell count falls within the normal range, which can vary slightly by laboratory and by factors such as your age and sex. A low count may suggest anemia, bleeding, or a shortage of iron, vitamin B12, or folate, while a high count can be linked to dehydration, lung or heart conditions, or other disorders that may need further evaluation. An abnormal result does not always mean something serious, so your doctor will look at the number along with your symptoms, medical history, and other test results before discussing what it means and what steps, if any, come next.

Results are compared to standard ranges for your age, sex, and health status. Low RBC counts may indicate anemia or blood loss, while high counts could signal conditions like dehydration or polycythemia. Your doctor will interpret results in the context of your medical history.