2.1.1 Research material
Data of newborn PKU screening in Shaanxi province, China, were acquired from the “National
Newborn Disease Screening Information Direct Reporting System,” and data were taken from 11 newborn disease screening reports in Shaanxi province from 2010 to 2018. Mutations in the PAH gene were present in 84 cases of PKU diagnosed by Shaanxi Neonatal Screening Center from 2010 to 2018.
2.1.2 Sample collection According to the requirements of the “Technical Specifications for Blood Collection for Neonatal Disease Screening” issued by the Chinese Ministry of Health (6), blood was collected between 72 h after birth and the first full breast feeding. Peripheral blood 0.5 ml was collected from the inner (or outer) edge of the heel of the newborn. The first drop of blood was discarded and another drop was applied to osmotic filter paper (903) for neonatal disease screening (diameter of the blood spot on both sides of the paper ≥8 mm). The filters were then air-dried, placed in a sealed bag, and stored at −80°C.