Laboratory tests in the differential diagnosis of hyperamylasemia.

We evaluated the clinical utility of some recently developed laboratory methods, including total amylase by three methods; isoamylase by inhibition and isoelectric focusing; lipase by pH-Stat and turbidimetry; and immunoreactive trypsin. All methods correlated highly positively with hyperamylasemia due to primary acute pancreatitis. Pancreatic-type isoamylase determinations have the greatest clinical usefulness, because total amylase, lipase, and immunoreactive trypsin are increased in a relatively high percentage of other abdominal diseases. Increases in the last-mentioned enzymes in nonpancreatic abdominal disease may be the result of injuries to the pancreas secondary to the primary disease, which are being detected with these highly sensitive methods. Because of the high clinical sensitivity of lipase and immunoreactive trypsin determinations, a normal result tends to exclude acute pancreatitis. Hyperamylasemia seen in lung carcinoma is due to increase in an amylase isoenzyme similar to the salivary-type amylase. The method for pancreatic-type isoamylase based on selective inhibition is satisfactory for routine clinical laboratory use.