Red Blood Cell Count (RBC)
Number of red blood cells per volume of blood
20 of 22 providers
Complete Blood Count (CBC)
Men:4.5-5.5 million/μL, Women:4.0-5.0 million/μL
What is Red Blood Cell Count (RBC)?
Red Blood Cell Count (RBC) measures the number of red blood cells (erythrocytes) per microliter of blood. Red blood cells are the most abundant cells in blood, with normal counts of 4.5-5.5 million/μL in men and 4.0-5.0 million/μL in women. Each RBC lives about 120 days, and your bone marrow produces approximately 2 million new RBCs every second to replace those that die.
RBCs are produced in bone marrow under the control of erythropoietin (EPO), a hormone released by kidneys in response to low oxygen. Each RBC contains hemoglobin, the iron-rich protein that binds and transports oxygen from lungs to tissues and carbon dioxide back to lungs. RBC count works together with hemoglobin and hematocrit to assess oxygen-carrying capacity and diagnose anemias or polycythemia.
RBC count varies by altitude (higher at elevation due to lower oxygen), hydration status, and individual physiology. Athletes and people living at high altitude typically have higher counts as an adaptation. Low RBC (anemia) causes fatigue and reduced exercise capacity, while high RBC (polycythemia) increases blood viscosity and clot risk. RBC count alone is less informative than hemoglobin or hematocrit, but combined with RBC indices (MCV, MCH, MCHC), it helps classify anemia types.
Why RBC Count Reveals Oxygen Delivery Capacity
- Anemia detection:Low RBC indicates anemia, but must be interpreted with hemoglobin and MCV to determine cause (iron deficiency, B12 deficiency, etc.)
- Polycythemia screening:High RBC (>5.5-6.0 million) suggests polycythemia vera, chronic hypoxia, or dehydration. Increases stroke and clot risk
- Oxygen delivery assessment:Combined with hemoglobin, indicates tissue oxygen delivery capacity. Critical for athletes and those with heart/lung disease
- Bone marrow function:Reflects bone marrow's ability to produce RBCs. Low production suggests marrow failure, while high production may indicate compensation for blood loss or hemolysis
- Altitude adaptation:RBC increases at high altitude are normal physiologic response. Helps distinguish pathologic from adaptive polycythemia
- Guide transfusion decisions:Very low RBC with severe anemia may require blood transfusion, especially if symptomatic or actively bleeding
Optimal vs Standard Ranges
OptimalMen:4.7-5.5 million/μL, Women:4.2-5.0 million/μL▼
Optimal oxygen-carrying capacity and tissue perfusion.
SuboptimalMen:4.2-4.7 million/μL, Women:3.8-4.2 million/μL▼
May indicate mild anemia or early deficiency states.
LowMen:<4.2 million/μL, Women:<3.8 million/μL▼
Indicates anemia requiring evaluation for iron, B12, or folate deficiency.
HighMen:>5.8 million/μL, Women:>5.3 million/μL▼
May indicate polycythemia, dehydration, or chronic hypoxia.
Scientific Evidence
Hemoglobin vs RBC Count in Anemia
While RBC count is useful, hemoglobin concentration is the preferred marker for defining anemia severity. WHO defines anemia as hemoglobin <13 g/dL in men and <12 g/dL in women, regardless of RBC count. Some anemias (thalassemia) have high RBC count but low hemoglobin due to small, poorly hemoglobinized cells. Clinical decisions should be based primarily on hemoglobin, not RBC count.
Polycythemia and Thrombosis Risk
Patients with polycythemia vera have 2-3 fold increased risk of thrombotic events (stroke, MI, DVT, PE). The CYTO-PV trial showed that maintaining hematocrit <45% with phlebotomy reduces thrombosis risk by 50% compared to <50% target. Low-dose aspirin further reduces thrombosis by 30-40%. These findings establish hematocrit <45% as the treatment target.
High Altitude Polycythemia
Healthy individuals at high altitude (>8,000 ft) develop physiologic polycythemia to compensate for reduced oxygen. RBC count can reach 6-7 million/μL. However, excessive polycythemia (hematocrit >60%) can impair oxygen delivery due to hyperviscosity. Chronic mountain sickness occurs when polycythemia becomes maladaptive. Treatment involves descent, phlebotomy, or acetazolamide.
Source:León-Velarde F, et al. Consensus statement on chronic and subacute high altitude diseases. High Alt Med Biol. 2005;6(2):147-157.
RBC Indices in Anemia Classification
RBC count combined with MCV (mean corpuscular volume) classifies anemias:Microcytic (low MCV <80 fL) with low RBC suggests iron deficiency or thalassemia. Macrocytic (high MCV >100 fL) with low RBC suggests B12/folate deficiency. Thalassemia trait shows low MCV but near-normal or mildly reduced RBC count (index:MCV/RBC <13 suggests thalassemia). This pattern recognition guides targeted testing.
Source:Hoffbrand AV, et al. Essential Haematology. 7th edition. Wiley-Blackwell. 2016.
Anemia and Cardiovascular Outcomes
Even mild anemia (hemoglobin 10-12 g/dL, RBC 3.5-4.0 million) increases cardiovascular risk by 20-40%. In patients with heart failure or coronary disease, anemia impairs oxygen delivery to myocardium, increases cardiac work, and worsens outcomes. However, aggressive treatment with ESAs to normalize hemoglobin has not improved outcomes and may increase thrombosis risk. Target hemoglobin 10-11 g/dL in symptomatic patients.
Source:Anand IS, et al. Anemia and change in hemoglobin over time related to mortality and morbidity in patients with chronic heart failure. Circulation. 2005;112(8):1121-1127.
Which Providers Test Red Blood Cell Count (RBC)?
Full Provider Comparison
| Provider | Includes | Annual Cost | Biomarkers |
|---|---|---|---|
 Superpower | ✓ | $199 | 100+ (150 with ratios) |
 WHOOP Advanced Labs | ✓ | $349 | 65 |
 Labcorp OnDemand | ✓ | $398 | 30+ |
| ✓ | $486 | 40+ | |
| ✓ | $444 | 288 | |
| ✓ | $349 | 100+ | |
| ✓ | $761 | 54 | |
 Function Health | ✓ | $365 | 160+ |
| ✓ | $250 | 65 | |
| ✓ | $495 | 70+ | |
| ✓ | $895 | 100+ | |
| ✓ | $1950 | 150+ | |
| ✓ | $375 | 80+ | |
| — | $Varies | 75+ | |
| ✓ | $190 | 100+ | |
| ✓ | $99 | 50 | |
| — | $124 | 60 | |
| ✓ | $199 | 50 | |
| ✓ | $499 | 120+ | |
| ✓ | $4188 | 70-80+ | |
| ✓ | $375 | 85 | |
| ✓ | $700 | 128 |
Frequently Asked Questions
What is Red Blood Cell Count (RBC)?
Number of red blood cells per volume of blood
What is the optimal range for Red Blood Cell Count (RBC)?
The standard reference range for Red Blood Cell Count (RBC) is Men:4.5-5.5 million/μL, Women:4.0-5.0 million/μL. Optimal ranges may differ based on individual health goals and expert recommendations.
Which blood test providers include Red Blood Cell Count (RBC)?
20 out of 22 blood testing providers include Red Blood Cell Count (RBC) in their panels. This biomarker is widely available across major providers.
What category does Red Blood Cell Count (RBC) fall under?
Red Blood Cell Count (RBC) is categorized under Complete Blood Count (CBC). This category includes biomarkers that help assess related aspects of health and wellness.
Medical Disclaimer
This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs.
Last reviewed:2026-02-20