Haemoglobin

Women: 120 to 150 g/L · Men: 130 to 170 g/L

Ranges differ by sex, in pregnancy and in childhood, and a little between laboratories; use the range your lab printed.

Haemoglobin is the protein inside red blood cells that carries oxygen from the lungs to the rest of the body. The test measures how much of it is present in a given volume of blood. A low haemoglobin is what doctors mean by anaemia.

It is the main measure doctors use when they want to know whether someone has enough red blood cells. It is part of the full blood count, one of the most commonly requested tests, and is often repeated to follow a trend.

• Dehydration on the day of the test
• Smoking
• Living or training at altitude
• Some lung and heart conditions
• Testosterone and some other hormone medicines
• Conditions where the bone marrow makes too many red cells

• Blood loss, including heavy periods
• Low iron, vitamin B12 or folate
• Pregnancy, because the blood volume expands
• Long-term kidney disease
• Long-term inflammatory illnesses
• Some medicines, including chemotherapy
• Bone marrow conditions

• Drinking a lot of fluid before the test can lower it slightly
• Being dehydrated can raise it slightly
• A sample taken lying down reads a little lower than one taken sitting
• It sits a little lower in the general population in older age and in pregnancy

No fasting needed. A single result is less informative than the trend over time.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.