A False-positive Newborn Screening Result: Goat's Milk Acidopathy

To the Editor.—With the increase in the number of diseases screened in newborn screening (NBS) programs, an increase in false-positive results has been noted.1 We encountered a 12-day-old female patient who presented with a positive NBS result for maple syrup urine disease secondary to goat milk consumption.Our patient initially had NBS results that revealed an elevated phenylalanine level (2.5 mg/dL [reference: <2.3 mg/dL]); thus, the filter-paper test was repeated and showed elevated valine (637 nmol/mL [reference range: 93–321 nmol/mL]) and leucine (381 nmol/mL [reference range: 42–188 nmol/mL]) levels. At 12 days of age, this infant was growing and feeding well without lethargy. The infant had been started on undiluted goat's milk, feeding every 3 to 4 hours since birth, because of a family history of cow's milk intolerance. Initial testing results were consistent with metabolic acidosis (bicarbonate: 17 mmol/L), an elevated serum urea nitrogen level (34 mg/dL [reference range: 20–24 mg/dL]), and no alloisoleucine but twice the normal valine, leucine, and isoleucine levels (505, 249, and 120 nmol/mL, respectively [reference range for each: 17–106 nmol/mL]).Electrolyte levels and acidosis resolved on soy formula and hydration overnight (bicarbonate: 25 mmol/L; serum urea nitrogen: 22 mg/dL). As a result, the findings were felt to be consistent with goat's milk acidosis secondary to elevated protein and acid load on the infant's kidneys. Harrison et al2 described a similar patient in 1979 whose condition also resolved with hydration and a more appropriate feeding regimen. With the increased sensitivity in NBS, this report adds to the list of possible dietary causes for false-positive NBS results. Because false-positive NBS results increase parental anxiety and can change parent-child relationships, recognition of possible dietary causes is important.1,3,4