Newborn screening for phenylketonuria: predictive validity as a function of age.

Area of Science:

• Biochemistry
• Genetics
• Neonatal Medicine

Background:

• Newborn screening programs aim to detect metabolic disorders like phenylketonuria (PKU) early.
• Phenylketonuria is a genetic disorder that can cause intellectual disability if untreated.
• The effectiveness of newborn screening can be influenced by factors such as infant age at sampling.

Purpose of the Study:

• To evaluate the predictive validity of newborn screening for PKU based on infant age.
• To determine how different blood sampling times affect PKU detection rates.
• To inform the development of improved newborn screening strategies for PKU.

Main Methods:

• Retrospective analysis of questionnaire data from 109 infants with PKU and 114 controls.
• Comparison of phenylalanine levels in cord blood and postnatal samples at various ages (days 1, 2, 4-7).
• Prediction of detection rates using screening cutoffs of 2, 4, and 6 mg/dL at different age intervals.

Main Results:

• Infants with PKU consistently showed phenylalanine levels below 4 mg/dL in all tested samples.
• Using a 4 mg/dL cutoff, approximately 33% of PKU cases would be missed with samples taken within the first 12 hours of life.
• Nearly 10% of PKU cases would be missed if samples are taken in the second 12 hours of life.

Conclusions:

• Newborn screening for PKU is not infallible and can miss a significant proportion of cases.
• The timing of blood sample collection is critical for accurate PKU screening.
• Early nursery discharges necessitate careful consideration in designing effective PKU screening protocols.