A heel prick blood test is carried out on all babies. It is taken when feeding has been established, usually between the fifth and the ninth day after birth. Initially it was used to screen for phenylketonuria, but it is now also used to diagnose hypothyroidism, haemoglobinopathies and other rare disorders.
Thyroxine is a hormone that is involved in the healthy functioning of most systems of the body. Hypothyroidism (when thyroxine levels are low) is one of the few preventable causes of severe learning difficulties. Early treatment is essential to avoid problems, and treatment with thyroxine (orally) needs to be continued for life. Hypothyroidism occurs in 1 in 4000 births.
Haemoglobinopathies are a group of inherited disorders where there is an abnormality in the structure of haemoglobin (the oxygen-carrying part of the blood). Sickle cell disease and thalassaemia are the best known of these disorders. In these disorders, the haemoglobin molecule is prone to deformity and destruction, which can result in pain, anaemia and jaundice. Being aware of these disorders early helps to avoid problems and to ensure prompt and appropriate treatment when necessary.
If the test for haemoglobinopathies is negative, it will always be so. However, a normal thyroid test in a newborn just means that the baby is not suffering from a thyroid disorder at this time. Many adults develop thyroid abnormalities in their lives. However, the condition is generally easier to diagnose in adulthood and the associated risks less extreme.