Certain high-protein infant diets may cause elevated levels of the amino acids tyrosine and phenylalanine, which may in turn produce a positive test result for a metabolic disorder, according to the findings of two case reports described in the Journal of Pediatrics.

The first case involved a full-term male infant who tested positive for phenylketonuria (PKU) at 7 days of age, lead author Dr. Chulaluck Techakittiroj, from Tulane University in New Orleans, and colleagues note. However, when first tested between 24 and 48 hours of life, the results were negative.

Initially, the child was fed with Enfamil, but because of spitting up and jaundice, he was changed to a higher protein formula, Shaklee Slim Plan Drink Mix, on day 5. Aside from elevated tyrosine and phenylalanine levels, the child appeared normal at 2 weeks. Transient elevated tyrosine levels were detected but after changing to a lower protein diet, Isomil, the levels quickly returned to normal.

The second case involved a female infant with a similar history. In this case, however, the high protein diet was Pet evaporated milk. A switch to Similac brought the elevated tyrosine and phenylalanine levels back down.

In each case, the high protein diets provided around 8 g/kg per day of protein, whereas the standard formulas provided about 4 g/kg per day, the report indicates.

“These cases highlight the importance of following infant nutritional guidelines,” the authors state. “Both patients were normal at the time of diagnosis, but the long-term effects of high protein intake in infants have not been” adequately studied, they add.

SOURCE: Journal of Pediatrics, February 2005.