Could my child get a positive newborn screening result, but not have phenylketonuria (a false positive)?
Yes. False positives occur because the test is designed to be very sensitive in detecting elevated phenylalanine levels. If your child receives a positive screening test, he or she will need another test to confirm the high phenylalanine level. If the level remains high, your child may have phenylketonuria or some other form of high phenylalanine. The other forms of high phenylalanine are also caused by changes in the PAH gene, but the symptoms are much milder than PKU. Could my child get a negative newborn screening result, but have phenylketonuria (a false negative)? Yes, but the false negative rate is extremely low. The newborn screening looks at the level of phenylalanine in the baby’s blood. Phenylalanine comes from protein, so the baby will not have any detectable change in the phenylalanine level until protein is consumed. Babies get protein from breast milk or infant formula. The more protein they eat, the higher the phenylalanine level. A false negative can come about if a bab
