Evolution of pancreatic function during the first year in infants with cystic fibrosis.

To describe pancreatic function during the first year of life in infants diagnosed with cystic fibrosis (CF) using serial fecal elastase measurements. This was a longitudinal study of 82 infants diagnosed with CF through newborn screening. Monthly stool samples were sent to a central laboratory for fecal elastase measurements. A total of 61 infants had an initial stool sample obtained at age <3.5 months and a final stool sample obtained at age >9 months. Twenty-six of 29 infants with a fecal elastase value <50 μg/g at study entry had a fecal elastase value <200 μg/g (the accepted cutoff value for pancreatic insufficiency) on all measurements during the year; all 29 had a value <200 μg/g at the end of the study. Of the 48 infants with initial fecal elastase value <200 μg/g, 13 had at least 1 fecal elastase value >200 μg/g but had a final stool fecal elastase value <200 μg/g; however, 4 infants with an initial fecal elastase value <200 μg/g ended the year with a value >200 μg/g. Eleven of 13 infants with an initial fecal elastase value of >200 μg/g still had a value >200 μg/g at the end of the first year. Infants with CF exhibit variability in fecal elastase values during the first year. Infants with a fecal elastase level of 50-200 μg/g at diagnosis should be treated with pancreatic enzyme replacement therapy, but fecal elastase should be remeasured at age 1 year to ensure that those with a falsely low value do not continue to receive pancreatic enzyme replacement therapy unnecessarily. Those with a fecal elastase value >200 μg/g initially can become pancreatic insufficient with time.