Colorimetric plasma assay for the bentiromide test (BT-PABA) for exocrine pancreatic insufficiency

Bentiromide is a synthetic peptide, N-benzoyl-L-tyrosyl-p-aminobenzoic acid, which has been used as a test for exocrine pancreatic function. Following oral administration, bentiromide is hydrolyzed by chymotrypsin to yield free p-aminobenzoic acid (PABA) which is absorbed, conjugated and excreted in the urine. The PABA conjugates reach their peak levels in blood in 90-120 min. Healthy individuals have higher levels of PABA than patients with pancreatic insufficiency. A simple, accurate, and precise method for the determination of PABA in blood has been developed and validated. The plasma (1 ml) is deproteinized by perchloric acid. The conjugates are hydrolyzed and the total PABA is determined colorimetrically by the Bratton-Marshall test. The standard curve in plasma is linear up to 8 micrograms/ml of PABA. A similar semimicro method using 200 microliter of plasma suitable for pediatric samples shows comparable results. Average analytical recovery is 97% and precision studies of pooled within-run and total between-run showed CV% of 5.0 and 5.7%, respectively.