Anaemia is diagnosed using a test that measures the level of haemoglobin in the blood. Haemoglobin is a pigment in red blood cells that binds oxygen and colours blood red. Normal levels are 12–16 g/dl in healthy women and 14–18 g/dl in men. The World Health Organisation (WHO) defines anaemia as a haemoglobin concentration below 11 g per decilitre of blood.