Hemoglobin

What is Hemoglobin?

Haemoglobin is the oxygen-carrying protein in your red blood cells. It picks up oxygen in your lungs and delivers it around your whole body: like a fleet of little delivery vans. A healthy value makes sure your tissues get enough oxygen, which feeds your energy and stamina.

Clinical frame

Haemoglobin determines the oxygen-carrying capacity of the blood and defines anaemia: in adults below 13 g/dL in men and below 12 g/dL in non-pregnant women. These WHO thresholds are statistical lower limits of a reference population, not outcome-based limits, and were recently re-established with international data ^[1].

In primary care, iron deficiency, anaemia of chronic disease and B12 or folate deficiency are the most frequent causes. In older people a third remains unexplained. The MCV guides the first classification (microcytic, normocytic, macrocytic), but does not rule out a deficiency. Ferritin and transferrin saturation confirm iron deficiency, also in the presence of inflammation ^{[2] [3]}.

A mildly reduced haemoglobin is rarely harmless: it goes with fatigue and reduced exercise tolerance, predicts more illness and death in older people, and is often the first signal of a treatable cause such as occult blood loss, an incipient deficiency, chronic inflammation or kidney disease. It therefore warrants targeted diagnostics, not reassurance ^{[3] [2]}.

What moves this value?

Iron deficiency, blood loss or a period of inflammation can lower it; dehydration can make it appear temporarily higher.

Iron-rich food with a little vitamin C and good hydration support a healthy value. Discuss a persistently low value with your doctor.

What this connects

• Ferritin

References

1. Braat, S. et al. Haemoglobin thresholds to define anaemia from age 6 months to 65 years: estimates from international data sources. Lancet Haematol 11, e253–e264 (2024). doi.org/10.1016/S2352-3026(24)00030-9
2. Auerbach, M., DeLoughery, T. G. & Tirnauer, J. S. Iron Deficiency in Adults: A Review. JAMA 333, 1813–1823 (2025). doi.org/10.1001/jama.2025.0452
3. Guralnik, J. et al. Unexplained anemia of aging: Etiology, health consequences, and diagnostic criteria. J Am Geriatr Soc 70, 891–899 (2022). doi.org/10.1111/jgs.17565