You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is A screening test for phenylketonuria (PKU) is performed on umbilical cord blood from a fair-skinned blond, blue-eyed infant born to dark-complexioned parents. The test is repoed as negative, and no dietary restrictions are imposed. At 1 year of age, the child is seen again, this time with obvious signs of severe mental retardation, and a diagnosis of PKU is made. The diagnosis was missed at bih because and explain in detail?
The concentration of phenylalanine in affected infants is usually normal at bih and increases rapidly during the first days of life. False-negative results are common immediately after bih but are rare on the second and third days of life. Consequently, the blood sample for phenylketonuria is usually taken from the infant's heel within 2 to 3 days after bih. If the test is performed too early, the diagnosis could be missed.