Evaluation of an inhibitor assay to determine serum isoamylase distribution.

We tested a technique to distinguish salivary from pancreatic isoamylase using a wheat protein which inhibits salivary isoamylase. The inhibitor technique accurately reflected the preponderance of pancreatic or salivary isoamylase in sera which had been "spiked" with human pancreatic or salivary isoamylase. Comparison of the results of either cellulose acetate electrophoresis or isoelectric focusing showed an excellent correlation (r = 0.99) in 43 hyperamylasemic sera which did not contain macroamylase. Normal values obtained in 160 healthy subjects indicated that pancreatic isoamylase comprised 41 +/- 21% (1 SD) of total serum amylase activity and the upper limit of normal for serum pancreatic isoamylase was 166 IU/liter. The inhibitor assay provides a simple and accurate means of differentiating salivary from pancreatic hyperamylasemia.