In vitro and in vivo analysis of the PABA test compared with the Lundh test--influence of intraluminal pH.

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Abstract
Lundh test and PABA [p-aminobenzoic acid) test results were compared in 50 patients. In the resulting correlation curve, 3 areas of interest were differentiated: an area with mean tryptic activity, found in the Lundh test, below 4 U/ml, where an abnormal PABA test result was also seen; an intermediate area from 4-9 U/ml, where PABA test results may be found in discordance with the Lundh test; the normal level, where PABA excretion was independent of intestinal chymotrypsin, activity. In in vitro experiments on the kinetics of the BTPABA (N-benzoyl-L-tyrosyl-p-aminobenzoic acid) hydrolysis by chymotrypsin the profound influence of the pH on Km and Vmax was shown. This influence of the pH explains why in the intermediate area of pancreatic dysfunction normal PABA test results were found in a number of cases. A higher mean pH level of the Lundh test aspirates was found for patients with a normal PABA test result than for patients with an abnormal PABA test.