Phenylketonuria is a treatable hereditary metabolic disease, where our primary goal is early diagnosis and treatment. Currently, a universal newborn screening system has been widely implemented. The standard procedure requires that after three days of breastfeeding, peripheral blood is collected from the newborn's heel, dropped onto specialized blood collection filter paper, and, once dried, sent to a screening laboratory to measure the phenylalanine concentration. If the phenylalanine concentration exceeds the cutoff value, further differential diagnosis and confirmation are conducted. Treatment typically starts two to three weeks after birth, and the prognosis is good. Additionally, diagnostic tests for phenylketonuria include urine ferric chloride, 2,4-dinitrophenylhydrazine tests, urinary purine profile analysis, and tetrahydrobiopterin loading test. Another method is through DNA analysis.