Red Blood Cells (RBC / Erythrocytes)
Cells that carry oxygen throughout your body. Low counts indicate anemia; high counts may suggest dehydration or other conditions.
What are Red Blood Cells?
Red blood cells (RBCs), also called erythrocytes, are the most abundant cells in your blood. Their primary function is carrying oxygen from your lungs to every tissue in your body and returning carbon dioxide for exhalation.
RBCs contain hemoglobin, the iron-rich protein that binds oxygen. A healthy adult has about 4–6 million RBCs per microliter of blood.
Normal Ranges
| Group | RBC Count |
|---|---|
| Adult men | 4.5–5.5 million/µL |
| Adult women | 4.0–5.0 million/µL |
Why It Matters
Anemia Detection
Low RBC count indicates anemia — insufficient oxygen-carrying capacity. This causes fatigue, weakness, and shortness of breath.
Polycythemia Detection
High RBC count (polycythemia) thickens blood, increasing clot risk. Causes include dehydration, lung disease, and bone marrow disorders.
Overall Health Assessment
RBC count is part of the complete blood count (CBC), one of the most common and informative blood tests.
Low RBC Count (Anemia)
Causes include:
- Iron, B12, or folate deficiency
- Chronic disease
- Blood loss
- Bone marrow problems
- Kidney disease (reduced EPO production)
High RBC Count (Polycythemia)
Causes include:
- Dehydration (most common)
- Chronic hypoxia (lung disease, high altitude, smoking)
- Polycythemia vera (bone marrow disorder)
- EPO-producing tumors
RBC Indices
The CBC includes related measurements:
- MCV — Average cell size
- MCH — Average hemoglobin per cell
- MCHC — Hemoglobin concentration
- Hematocrit — Percentage of blood volume
Related Biomarkers
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