Hemoglobin
Oxygen-carrying protein in red blood cells
Also known as
Definition
Hemoglobin is the iron-containing protein in erythrocytes that transports oxygen from the lungs to tissues. Low levels define anemia and may manifest as fatigue, pallor, and reduced physical performance. Hemoglobin is routinely measured in a complete blood count and is a core vital parameter for assessing oxygen-carrying capacity.
| Parameter | Value |
|---|---|
| Unit | g/dl |
| Reference Range | Women: 12.0–16.0 g/dl | Men: 13.5–17.5 g/dl |
| Optimal Range (lab2go) | Women: 13.0–15.5 g/dl | Men: 14.5–16.5 g/dl |
↓ What a low value means
Hemoglobin below sex-specific reference values defines anemia (WHO: women < 12.0 g/dl, men < 13.0 g/dl). Mild anemia (Hb 10–12/13 g/dl): fatigue, pallor, reduced exercise capacity. Severe anemia (Hb < 8 g/dl): tachycardia, dyspnea, cognitive impairment. Causes: iron deficiency (most common worldwide), vitamin B12/folate deficiency, chronic disease, blood loss, hemolytic disorders.
↑ What a high value means
Elevated hemoglobin (> 16 g/dl women, > 18 g/dl men) occurs in polycythemia vera (myeloproliferative), reactive polycythemia (altitude, smoking, COPD, sleep apnea), or doping (EPO). Risks: elevated blood viscosity, thromboembolic hazard. Athletes at altitude may physiologically show elevated values.
✓ How to optimize this marker
For iron-deficiency anemia: iron-rich diet (meat, legumes, leafy greens), vitamin C to boost absorption, separate tea/coffee from meals. Ferrous iron supplementation per medical indication (alternate-day dosing for better absorption). For B12/folate anemia: appropriate supplementation. Clarify the cause before treating symptoms.
When to test
In the complete blood count (CBC), routinely determined during check-ups. No fasting required. For known anemia: follow-up after 4–8 weeks of therapy. Pregnant: screening each trimester. Athletes: annually.
Frequently asked questions
What is the difference between hemoglobin and ferritin? +
Ferritin reflects iron stores and falls before hemoglobin with deficiency. Hemoglobin only falls when stores are largely depleted. Low ferritin with normal hemoglobin = latent iron deficiency without anemia — but already with symptoms like fatigue.
Can I exercise with anemia? +
Mild anemia (Hb 10–12 g/dl) allows moderate exercise but limits maximal performance. With severe anemia (Hb < 8 g/dl), intense exercise should be avoided until treated. Always clarify the cause medically first.
How quickly does hemoglobin rise after iron therapy? +
Hemoglobin typically begins rising after 2–4 weeks of oral iron therapy and normalizes after 4–8 weeks. Replenishment of ferritin stores takes an additional 3–6 months after Hb normalization.
Sources
Last Reviewed: May 28, 2026 · sina
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.