The patient is exhibiting signs of phenylketonuria, despite a normal newborn screen. A false negative may occur if the neonate had not eaten at all or enough prior to the screening being performed. The most appropriate action is to obtain blood to be tested for phenylalanine in the hospital lab. An additional newborn screen sent to the state lab takes a significant amount of time, during which the patient’s condition may worsen. A partially hydrolyzed formula is not the appropriate substitute for the neonate with PKU; there are formulas specifically designed to not have phenylalanine. Although it is helpful to know if the baby had eaten prior to the newborn screen, tracking down the nurse to ask him or her about something that happened 16-18 days ago wastes valuable time.