Red Blood Cell Count (RBC)

Routine annual

also erythrocyte count

What it isThe number of red blood cells per microliter of blood. Red cells are made in the bone marrow under the control of erythropoietin from the kidneys and live about 120 days.

DoesCarry oxygen from lungs to tissues and carbon dioxide back.

GoodA mid-range RBC count reflects healthy marrow, sufficient iron and B vitamins, and adequate kidney signaling.

BadLow RBC means anemia — fatigue, reduced exercise capacity, cognitive fog. High RBC (polycythemia) raises clotting risk and is sometimes driven by sleep apnea, smoking, or testosterone therapy.

Standard

Men 4.5–5.9 M/µL; women 4.0–5.2 M/µL.

Optimal

4.8–5.4 M/µL men, 4.3–4.9 M/µL women (narrow target)

Modifiers

Rises at altitude and with testosterone; falls with iron deficiency, chronic disease, or marrow disorders.

How to optimize

Lifestyle: Quality sleep; treat sleep apnea (drives polycythemia); altitude training raises it acutely.
Diet: Adequate iron, B12, folate, and protein from whole foods — red meat, eggs, leafy greens, legumes.
Supplements: Iron (only if deficient), methylcobalamin (1000µg/day), methylfolate (400–800µg/day).
Peptides: —
Drugs: Treat underlying cause; phlebotomy for high counts; erythropoiesis-stimulating agents only for documented anemia.

within Blood Cells