Glossary term
Red Blood Cells
Also known as: RBC, Erythrocytes
Part of: Blood Test Results
- Reading time
- 4 min read
- Last reviewed
- Last reviewed January 1970
- Reading level
- Written in plain English
- Reviewed by
- Reviewed by Medipher Editorial Team
The cells in your blood that carry oxygen. They contain haemoglobin, which does the actual oxygen carrying.
Medipher explains medical wording in plain English — it does not diagnose or replace a clinician. If this is a medical emergency, call your local emergency number immediately.
Simple visual explanation
What is this?
Red blood cells (RBCs) are small, disc-shaped cells made in your bone marrow. Their main job is to carry oxygen from your lungs to your tissues and take carbon dioxide back to your lungs.
The RBC count on your blood test tells clinicians roughly how many of these cells you have in a small volume of blood. It is almost always looked at together with haemoglobin and the size of the cells (MCV).
Each red blood cell lives for around 120 days before being recycled in the spleen and liver, so your body constantly produces fresh ones — around two million every second.
Why is it important?
The RBC count helps identify anaemia (too few or too small cells) and less common conditions where the body makes too many cells.
Because RBCs carry oxygen, an abnormal count can help explain symptoms such as tiredness, breathlessness or dizziness — although these symptoms have many possible causes.
Trends over time carry more meaning than any single reading, especially when other blood-count values are within their expected ranges.
Where you'll see it: Full Blood Count (FBC / CBC) reports as RBC, usually alongside haemoglobin and MCV.
How doctors use this result
Clinicians may use this result to:
- Assess for anaemia together with haemoglobin and MCV.
- Explain non-specific symptoms such as fatigue or breathlessness.
- Screen before surgery, in pregnancy and during long-term illness monitoring.
- Track the response to treatment for anaemia or bone-marrow conditions.
What's the normal range?
| Adult women | 3.9–5.2 × 10¹²/L |
| Adult men | 4.5–5.9 × 10¹²/L |
Ranges vary by laboratory, age and pregnancy. Always use the range on your report.
Small variations from the printed range are common and often don't need action, especially if haemoglobin and MCV are normal.
Normal ranges are guides, not verdicts. Interpretation depends on your age, sex, symptoms, medical history, medications and other investigations — which is why your clinician looks at the whole picture rather than a single value.
Common reasons it may be high
Dehydration
Concentrates the blood so cell counts look higher than they truly are.
Smoking or high altitude
Both lower oxygen delivery, prompting the marrow to make more red cells over time.
Lung or heart conditions
Long-term low oxygen levels stimulate extra red-cell production.
Polycythaemia
A bone-marrow condition producing too many red cells; requires specialist assessment.
Common reasons it may be low
Iron, B12 or folate deficiency
These nutrients are needed to build normal red blood cells.
Blood loss
Obvious or hidden bleeding reduces the number of cells in circulation.
Chronic illness
Long-standing conditions can suppress red-cell production.
Pregnancy
Blood volume increases faster than cell numbers, giving a normal dilution effect.
Does an abnormal result always mean something is wrong?
Not necessarily. A number that sits outside the printed range is a prompt for interpretation — not a diagnosis.
- A single result rarely gives the full picture — clinicians interpret it alongside your symptoms.
- Your medical history, medications and other blood tests all shape the meaning of one value.
- Small movements just outside the reference range are common and often not concerning.
- Repeat testing over time is frequently more useful than any single number.
What might happen next?
- A repeat test to confirm.
- Iron studies, B12 and folate if anaemia is suspected.
- A specialist referral if the cause is unclear or the count is very abnormal.
One result rarely tells the whole story. Clinicians look at your symptoms, medical history, medications and other tests together — and a single value that sits slightly outside the reference range is often normal for you. Repeat testing over time is frequently more useful than any one number. Medipher helps you understand what a result means in plain English, but it cannot diagnose medical conditions or replace advice from a doctor, nurse or pharmacist.
When should I speak to a healthcare professional?
Speak with your GP or another healthcare professional if:
- You've been asked to repeat the test.
- You're experiencing new or worsening symptoms.
- Your clinician has flagged the result as needing follow-up.
- You don't understand your results or feel unsure what to do next.
If you have severe symptoms — chest pain, severe breathlessness, fainting, heavy bleeding or feel very unwell — seek urgent help. If this is a medical emergency, call your local emergency number immediately. Medipher is designed to help explain medical information and is not an emergency service.
Frequently asked questions
Related blood tests
Terms clinicians often look at alongside Red Blood Cells.
Related guides
Still unsure what your result means?
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Sources
General patient information referenced when writing this page.
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This glossary entry is general health information, not medical advice. Medipher explains medical wording in plain English and does not diagnose, provide treatment advice, or replace a GP, doctor, nurse or pharmacist. Always discuss your results with a qualified clinician.