Use of serum amylase isoenzymes in evaluation of pancreatic function.

Amylase isoenzyme patterns were evaluated in serum, urine, and duodenal fluid from 
19 patients with cystic fibrosis (CF) and normal subjects. Two thirds 
of the CF patients with absent pancreatic enzymes lacked a serum 
pancreatic isoamylase band, while the remainder had a markedly diminished pancreatic 
band when compared to the salivary isoamylase. In normal sera the 
pancreatic band is equal to or greater than the salivary band. 
In all patients with absent enzymes the diagnosis of abnormal pancreatic 
function could have been made by evaluation of serum isoamylase patterns 
thereby avoiding duodenal intubation or collection of 72-hour stools for proteolytic 
enzyme activities. The patients with normal pancreatic enzyme activities had normal 
serum zymograms. No CF patient had a low total serum amylase 
concentration. Total duodenal fluid amylase levels may be misleading in the 
evaluation of pancreatic function since the amylase may be of salivary 
origin. The advantages of this isoamylase method include (1) simplicity and 
noninvasiveness, requiring only a small blood sample; (2) specificity for pancreatic 
function; and (3) independence of pancreatic enzyme medication. 