Clinical meaning
Newborn screening (NBS) is a public health program designed to identify infants with serious but treatable genetic, metabolic, endocrine, and structural conditions before clinical symptoms develop. The rationale is based on the principle that early detection and treatment during the pre-symptomatic period can prevent intellectual disability, organ damage, metabolic crises, and death. The blood specimen for metabolic screening is collected via heel prick (capillary blood) and applied to a standardized filter paper card (Guthrie card). The blood is analyzed using tandem mass spectrometry (MS/MS), which can simultaneously screen for dozens of metabolic conditions from a single dried blood spot. The optimal collection window is 24-48 hours after birth; collection before 24 hours may yield false-negative results because the infant has not yet been exposed to sufficient protein feeding to trigger metabolic pathway abnormalities. Phenylketonuria (PKU) is an autosomal recessive disorder caused by a deficiency of phenylalanine hydroxylase (PAH), the hepatic enzyme that converts phenylalanine to tyrosine. Without this enzyme, phenylalanine accumulates to neurotoxic levels, causing irreversible intellectual disability, seizures, musty body odor, fair coloring (due to impaired melanin synthesis from...