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
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.
| Range Type | Level | Significance |
|---|---|---|
| Optimal | Men:4.7-5.2 million/μL, Women:4.2-4.8 million/μL | Ideal range for oxygen delivery without excessive blood viscosity. Indicates healthy bone marrow function, adequate iron/B12/folate stores, and normal kidney EPO production. Values in this range support optimal exercise capacity, energy levels, and cardiovascular health. |
| Borderline Low/High | Men:4.2-4.7 or 5.2-5.8 million/μL, Women:3.8-4.2 or 4.8-5.3 million/μL | Low-normal may indicate early anemia or dilutional effect (pregnancy, overhydration). Check hemoglobin, ferritin, B12, folate. High-normal may be physiologic (athletes, high altitude) or early polycythemia. If hemoglobin and hematocrit also borderline, investigate further. Retest in 3 months. |
| Anemia | Men:<4.5 million/μL, Women:<4.0 million/μL | Indicates anemia requiring investigation. Check MCV to classify:low MCV suggests iron deficiency, high MCV suggests B12/folate deficiency or alcohol use, normal MCV suggests anemia of chronic disease or blood loss. Evaluate with ferritin, iron studies, B12, folate, reticulocyte count. Consider bone marrow biopsy if cause unclear. |
| Polycythemia | Men:>5.8 million/μL, Women:>5.3 million/μL | Indicates polycythemia (too many RBCs). Increases blood viscosity and thrombosis risk. Causes:Polycythemia vera (bone marrow disorder producing excess RBCs), secondary polycythemia (chronic hypoxia from lung disease, sleep apnea, smoking), dehydration (concentrates RBCs), testosterone use, EPO-secreting tumors. Check hemoglobin, hematocrit, oxygen saturation, EPO level, JAK2 mutation (if polycythemia vera suspected). |
Iron deficiency (low MCV):Ferrous sulfate 325 mg 2-3x daily or IV iron if malabsorption. Investigate source of blood loss (GI bleeding, menorrhagia). Recheck RBC/hemoglobin in 4-8 weeks
B12 deficiency (high MCV):B12 1000 mcg IM weekly x 4-8 weeks, then monthly. Or oral B12 1000-2000 mcg daily. Address pernicious anemia or dietary insufficiency
Folate deficiency (high MCV):Folic acid 1-5 mg daily. Common in alcoholics, pregnant women, malabsorption
Anemia of chronic disease (normal MCV):Treat underlying condition (inflammatory bowel disease, rheumatoid arthritis, cancer, chronic kidney disease). Consider erythropoietin-stimulating agents (ESAs) if severe
Bone marrow failure:May require transfusions, immunosuppression, or stem cell transplant depending on cause
Polycythemia vera:Phlebotomy (blood removal) to keep hematocrit <45% in men, <42% in women. Aspirin 81 mg daily reduces clot risk. Hydroxyurea if high-risk (age >60, prior thrombosis)
Secondary polycythemia:Treat underlying cause. CPAP for sleep apnea, smoking cessation, supplemental oxygen for lung disease. Phlebotomy if hematocrit >54% and symptomatic
Dehydration:Rehydrate with 2-3 liters fluids daily. Recheck RBC after proper hydration—should normalize if dehydration was cause
Testosterone-induced:Reduce testosterone dose or stop if polycythemia develops. Target hematocrit <50-52%
High altitude:Physiologic adaptation, no treatment needed unless excessive (hematocrit >60%). Consider descent if symptomatic
Iron:Men 8 mg/day, women 18 mg/day (premenopausal). Food sources:red meat, spinach, lentils, fortified cereals. Vitamin C enhances absorption
Vitamin B12:2.4 mcg/day minimum. Food sources:meat, fish, dairy, eggs. Vegans need supplementation
Folate:400 mcg/day (800 mcg if pregnant). Food sources:leafy greens, legumes, fortified grains
Copper:900 mcg/day. Required for iron utilization. Sources:nuts, shellfish, whole grains
Vitamin B6:1.3-2.0 mg/day. Cofactor for hemoglobin synthesis. Sources:poultry, fish, potatoes, bananas
Protein:Adequate protein (1.0-1.2 g/kg) provides amino acids for globin chains in hemoglobin
Avoid bone marrow toxins:Excessive alcohol suppresses RBC production. Limit to <1-2 drinks daily or eliminate
Medication review:Chemotherapy, some antibiotics (chloramphenicol), anticonvulsants can suppress bone marrow. Monitor CBC regularly if on these medications
Treat infections:Parvovirus B19 can cause severe anemia (pure red cell aplasia). HIV, hepatitis suppress bone marrow
Optimize kidney function:Kidneys produce EPO. Chronic kidney disease (eGFR <30) reduces EPO, causing anemia. May need ESAs
Avoid lead exposure:Lead toxicity impairs heme synthesis and shortens RBC lifespan, causing anemia
Regular exercise:Moderate exercise stimulates EPO production and improves RBC efficiency. Intense endurance training may cause "sports anemia"(dilutional from increased plasma volume)
Altitude training:Living or training at altitude (>5,000 ft) naturally increases RBC count. Athletes use this to improve oxygen capacity
Adequate sleep:Sleep deprivation impairs EPO production and bone marrow function. Aim for 7-9 hours nightly
Hydration:Dehydration concentrates RBC. Proper hydration (30-35 ml/kg daily) ensures accurate RBC count
Avoid smoking:Smoking causes compensatory polycythemia (increased RBC due to carbon monoxide reducing oxygen delivery)
Blood donation:Regular donors may develop iron deficiency anemia. Supplement iron or space donations adequately
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.
Source:World Health Organization. Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity. Vitamin and Mineral Nutrition Information System. Geneva, 2011.
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.
Source:Marchioli R, et al. Cardiovascular events and intensity of treatment in polycythemia vera. N Engl J Med. 2013;368(1):22-33.
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 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.
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.
| Provider | Includes | Annual Cost | Biomarkers |
|---|---|---|---|
 Superpower | ✓ | $199 | 100+ (150 with ratios) |
 WHOOP Advanced Labs | ✓ | $349 | 65 |
 Labcorp OnDemand | ✓ | $398 | 30+ |
| ✓ | $486 | 40+ | |
| ✓ | $468 | 83 | |
| ✓ | $349 | 100+ | |
 InsideTracker | ✓ | $680 | 54 |
 Function Health | ✓ | $365 | 100+ |
| ✓ | $250 | 65 | |
| ✓ | $495 | 70+ | |
| ✓ | $895 | 100+ | |
| ✓ | $1950 | 150+ | |
| — | $399 | 100+ | |
| — | $Varies | 75+ | |
| ✓ | $190 | 100+ | |
| ✓ | $99 | 50 | |
| — | $125 | 60 | |
| ✓ | $199 | 50 | |
| ✓ | $499 | 120+ | |
| ✓ | $4188 | 80+ | |
| ✓ | $375 | 85 | |
| ✓ | $700 | 129 |
20 providers include this biomarker in their panels
This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs.
