Explainer · updated 2026-09-09

Haemoglobin, explained in plain English

Written by the medk.AI team · Last reviewed September 2026 by the medk.AI content team

Key facts

• Typical adult reference interval in women: 12-16 g/dL (ABIM)
• Typical adult reference interval in men: 14-18 g/dL (ABIM)
• Typical adult reference interval in women, in SI units: 119-157 g/L (HRI-HR)
• Typical adult reference interval in men, in SI units: 138-175 g/L (HRI-HR)

What it is

Haemoglobin is the protein inside your red cells that carries oxygen around the body. Anaemia is defined on this figure rather than on any other measurement, which makes it usually the first line a doctor reads in a blood count.

What the number is telling you

Levels differ between men and women, which is why reports carry separate reference rows for each. One reading says little; time and trend matter. A level that drifts down across several reports tells a different story from a single low result.

What high or low can mean

Low is where anaemia is drawn. The World Health Organization draws the line below 130 g/L in men and below 120 g/L in non-pregnant women aged 15 to 65. Iron in the diet is what rebuilds haemoglobin, and ongoing blood loss from any cause, heavy periods included, is a common reason it falls.

High that lasts usually means the body is making extra red cells to carry more oxygen. That pattern follows smoking, lung disease or living at altitude. Smoking is the one piece of it that habits can change.

What a typical result looks like

Typical adult reference intervals from ABIM run from 14 to 18 g/dL in men and from 12 to 16 g/dL in women. Outside the United States, reports often use grams per litre instead; one harmonised European set (HRI-HR) runs 138 to 175 g/L in men and 119 to 157 g/L in women. The range on your own report is the one that counts.

Questions worth asking your doctor

• Is this level low enough to act on, or is it being watched?
• Do my iron studies explain it, or should we look further?
• If my level is low, where might the blood loss be coming from?
• What could explain a level that stays high?

If a result worries you, ask your doctor.

Sources

• ABIM Laboratory Test Reference Ranges (2026)
• Verification of harmonized reference intervals in Croatia: is it time for a change? (2026)