Heel blood is the blood in the veins at the root of the foot. The clinical examination of heel blood is mainly performed on newborns born within 3-7 days, and no later than 20 days. It is mainly used to screen for phenylketonism (an autosomal recessive genetic disorder in which the baby’s phenylalanine metabolism is impaired and large amounts of phenylalanine are excreted in the urine) and hypothyroidism (congenital reduced thyroid secretion). This is because these two diseases, if not detected and treated early, can lead to impaired mental development, severe hypo and delayed development, etc. in children. Therefore, after the birth of a baby, parents are advised to actively cooperate with the doctor to do the screening of heel blood. Timely detection and early diagnosis are necessary to avoid delaying treatment and affecting their whole life.