Determination of the exocrine pancreatic function with the NBT-PABA test using a novel dual isotope technique and gas chromatography mass spectrometry

We describe a tubeless test of exocrine pancreatic function based on a new dual isotope technique, using N-benzoyl-L-tyrosyl-p-aminobenzoic acid (NBT-PABA) as a substrate for intestinal chymotrypsin activity and the stable isotope, C-13-PABA as marker. Gas chromatography-mass spectrometry (GC-MS) was used for the quantification of PABA and C-13-PABA in blood. The method involves hydrolysis, extractions, separation by HPLC, and methyl ester formation of the test substances before GC-MS analysis. The test is precise and shows good separation of healthy volunteers from patients with pancreatic insufficiency. The PABA/C-13-PABA ratios in serum after 1.5 h were 2.64 +/- 0.14 (mean +/- SEM) in 10 healthy volunteers and 1.26 +/- 0.22 in 10 patients with exocrine pancreatic insufficiency. We present a sensitive and specific assay, which is free of analytical interference and radiation hazards and, additionally, it illuminates extrapancreatic pharmacokinetic conditions. This test can eliminate the need for duodenal intubation, which makes it very acceptable to the patients.