From the Guidelines
PKU Newborn Screen Timing
It is recommended to perform the PKU newborn screen after 24 hours of life, as this allows for accurate detection of phenylketonuria 1.
- Screening before 24 hours may lead to false-negative results due to inadequate accumulation of phenylalanine.
- According to hospital protocols and state regulations, newborn metabolic screenings, including PKU, have been completed, but if performed before 24 hours of milk feeding, a system for repeating the test during the follow-up visit must be in place 1.
- Ideally, the screen should be done between 24 to 72 hours after birth, when the baby is at least 24 hours old and has been fed, to ensure accurate results.
- Accurate detection of phenylketonuria is crucial, and performing the screen too early may compromise this, hence the emphasis on waiting until after 24 hours of life 1.
From the Research
PKU Newborn Screening Timing
- The timing of Phenylketonuria (PKU) newborn screening has been a topic of discussion, with some studies suggesting that screening can be performed before 24 hours of life 2, 3.
- A study published in 1983 found that the sensitivity of the screening test rapidly increases with age, and a critical value of 3 mg/dL would be satisfactory for suspecting PKU at any age, if the Guthrie test were appropriately modified 2.
- Another study published in 1991 found that a newborn screening phenylalanine cutoff level of 2 mg/dL would have identified all neonates with PKU within the first 24 hours of life, but a cutoff level of 4 mg/dL would have missed 2 of the 6 with PKU before 24 hours of life 3.
- A 1997 study recommended that neonates be at least 12 hours of age before initial bacterial inhibition assay (BIA) PKU screening be carried out, due to concerns about the sensitivity of the screening test in early discharge specimens 4.
Screening Methods and Technologies
- Advances in screening technologies, such as tandem mass spectrometry (MS/MS) and direct analysis in real time (DART) mass spectrometry, have improved the accuracy and precision of PKU screening, allowing for earlier detection and reduced false-positive rates 5, 6.
- A 1998 study found that MS/MS analysis reduced the number of false-positive results from 91 to 3, and simultaneous quantification of phenylalanine and tyrosine by MS/MS further reduced the number of false positives to 1 5.
- A 2013 study developed a rapid and simple method for PKU screening using DART-TQ-MS/MS, which can analyze dried blood spot samples in 18 seconds per sample 6.