Breastfeeding effects on newborn screening

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To the Editor:

We read with interest the article by Santoro et al¹ on the amount of colostrum ingested by healthy newborns during the first 24 hours of life. Beyond their stated purpose to evaluate this variable as a predictor of successful breastfeeding, we believe their observation is also relevant to the timing of newborn screening sample collection. Early newborn discharge has led to newborn screening anticipation,² with blood specimens collected shortly after 24 hours of life. This study showed that the amount of colostrum ingested by exclusively breastfed newborns in the prescreening interval is 15 ± 11 g. Considering the colostrum protein composition,³ the cumulative intake by the time of blood specimen collection can be approximated to 0.2 g. This very small amount of exogenous protein is unlikely to cause an abnormal screening result in newborns affected by inborn errors of amino acid metabolism, such as phenylketonuria (PKU). Indeed, phenylalanine tolerance on PKU newborns may exceed by 20 to 40 times, from severe to benign phenotypes,⁴ the dietary phenylalanine intake during the first 24 hours of life. These findings validate the hypothesis that neonatal protein catabolism is the main determinant leading to abnormal screening outcomes in newborn with PKU.⁴ The low protein intake in the prescreening interval appears to be well below the exogenous protein tolerance (notwithstanding its wide variability) observed in urea cycle and branched chain amino acid disorders. These considerations are pertinent to many inborn errors of metabolism currently included in expanded newborn screening programs. Given the crucial role of neonatal protein catabolism in determining the outcome of newborn screening, attentive evaluation of potentially influencing factors may be relevant for the optimization of the timing of blood specimen collection, as well as for the interpretation of results.

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References 

1. Santoro W, Martinez FE, Ricco RG, Jorge SM. Colostrum ingested during the first day of life by exclusively breastfed healthy newborn infants. J Pediatr. 2010;56:29–32
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2. Friedman MA, Spitzer AR. Discharge criteria for the term newborn. Pediatr Clin North Am. 2004;51:599–618
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3. Räihä NCR. Protein content of human milk, from cholostrum to mature milk. In:  Räihä NCRR editors. Protein Metabolism During Infancy. New York: Raven Press; 1994;p. 211–228
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4. Ponzone A, Spada M, Roasio L, Porta F, Mussa A, Ferraris S. Impact of neonatal protein metabolism and nutrition on screening for phenylketonuria. J Pediatr Gastroenterol Nutr. 2008;46:561–569
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