Svetozár Dluholucký, Mária Knapková, Juraj Zbojan, Mária Mošková, Františka Hrubá
Background: In order to minimize the risk of false negativity many guidelines for PKU newborn screening recommend to obtain the blood sample only after sufficient protein intake, e.g. 4th, or 5th day after birth. However, this recommendation is not universal and many screening centers provide PKU screening regardless the age, and food intake, namely when the screening is performed by fluorometric method. The authors followed the trend of dry blood spot (DBS) phenylalanine levels in healthy full term newborns since birth to 6th day of life in comparison to milk intake and time after birth. Methods: DBS samples were taken from venous or capillary blood during other laboratory tests. The time of blood sampling and amount of ingested milk (breast, or cow milk formula) were recorded. Results: One hundred sixty two DBS samples from 117 healthy full term newborns were evaluated. There was no statistical significance in trend of phenylalanine levels to time after birth, to total amount of ingested milk, namely breast milk. Statistically significant positive correlation of amount of ingested cow milk formula and DBS phenylalanine level was found. Conclusion: There were no positive correlations of fluorometric DBS phenylalanine levels to time after birth, food intake, and amount of ingested milk, except cow milk formula. Despite an absence of the „positive control“ (PKU positive) the fluorometric method seems to be the reliable for early PKU screening – before 4th day of life.