Failure of p-aminobenzoic acid screening test to diagnose pancreatic insufficiency in Shwachman's syndrome.

The 6-h urine recovery of p-aminobenzoic acid (PABA) following the administration of a standard dose of N-benzoyl-L-tyrosyl-p-aminobenzoic acid (BTPABA) was performed in 13 control subjects and two siblings with Shwachman's syndrome. The control subjects showed a recovery of 67 +/- 12.1% (mean +/- 1 SD) of the administered dose, consistent with previously reported values. Unexpectedly, the recovery of PABA in two siblings with Shwachman's syndrome was found to be 67 and 63%, respectively. The values are well within the normal range. In these siblings, fecal chymotrypsin activities were very low when measured with N-acetyl-L-tyrosyl-ethyl ester (ATEE) as substrate, but were normal when BTPABA was the substrate. The duodenal juice of the younger affected child following pancreozymin-secretin stimulation showed very low chymotrypsin activity against ATEE, BTPABA, and N-benzoyl-L-tyrosyl-ethyl ester. These findings suggest that there may be BTPABA-splitting activity in the lower bowel of these siblings with Shwachman's syndrome. This activity might be that of enteric bacteria or of the intestinal mucosa.