Diagnosis of exocrine pancreatic insufficiency in cystic fibrosis by the synthetic peptide N-benzoyl-L-tyrosyl-p-aminobenzoic acid.

The synthetic peptide N-benzoyl-L-tyrosyl-p-aminobenzoic acid is specifically cleaved by chymotrypsin to Bz-Ty 
and PABA. The liberated PABA is absorbed and excreted in the 
urine. Accordingly, PABA recovery reflects intraluminal chymotrypsin activity and is an 
index of exocrine pancreatic function. This test was evaluated in 24 
patients with cystic fibrosis to determine its role in the diagnosis 
of exocrine pancreatic insufficiency. Cumulative percent PABA recovery in six hours 
was significantly lower in CF patients compared with the control group. 
No overlap was noted between the two groups. There was good 
correlation between PABA recovery, fecal chymotrypsin activity, and coefficient of fat 
absorption. These findings indicate that PABA recovery is significantly reduced in 
patients with CF and steatorrhea and may prove a practical and 
reliable test of pancreatic insufficiency. 