Phenylketonuria is a common autosomal recessive genetic disorder and the most common congenital amino acid metabolism disorder. It primarily manifests as intellectual disability, light skin and hair pigmentation, and a mousey urine odor. Newborn screening includes routine screening for phenylketonuria as it is a treatable hereditary metabolic disorder, emphasizing the importance of early diagnosis and treatment. Nowadays, newborn screening systems are widely implemented. Generally, this involves collecting a blood sample through a heel prick, dropping the blood on specialized filter paper, and then air drying before sending it to a screening laboratory to measure the phenylalanine concentration. Typically, a normal concentration should be less than 120 micromoles per liter. If the phenylalanine concentration exceeds 1200 micromoles per liter, it can be diagnosed as classical phenylketonuria.