PABA-test for diagnosis of exocrine pancreatic insufficiency [letter].

We have also found a significant difference between the 6-hour urinary PABA 
recovery in healthy controls and CF patients, with no overlap of 
the ranges, and a good correlation with fecal chymotrypsin activity. We 
can stress the usefulness of the test in this age group. 
In studying a group of healthy newborn infants, however, the results 
were quite different: The PABA recovery was smaller and showed greater 
variations and overlap with results in CF patients occurred. It is 
clear that the test is not applicable in newborn infants when 
performed in the described manner. One possible explanation is the physiologically 
limited glomerular filtration rate in the newborn infant, which could have 
delayed the PABA excretion. 