Phenylketonuria is an amino acid metabolic disorder caused by a genetic mutation and is often detected by newborn screening. In clinical screening for phenylketonuria in newborns, blood is usually taken from the end of the heel to detect phenylalanine concentration in the blood, and if it is higher than normal, prompt review is required. If the result is still above normal and other specific possibilities are excluded, the test is positive and can be combined with other test results to determine if the disease is present. Phenylalanine concentrations of 120-360 μmol/L are clinically defined as mild phenylketonuria, phenylalanine concentrations of 360-1200 μmol/L as moderate phenylketonuria, and phenylalanine concentrations greater than 1200 μmol/L as classic phenylketonuria. Children will have varying degrees of convulsions, dry skin, pale hair, eczematous rash, and delayed growth and development, and lag in intellectual development and language skills. Growing up, young children may also have poor mental status such as autism, hyperactivity, and low self-esteem, so timely treatment is required. This is usually done by improving the diet under professional guidance and, if necessary, by medication.