The role of serum isoamylase and lipase determinations in clinical practice.

To determine the clinical utility of routine determination of serum isoamylase (pancreatic/salivary) and/or lipase activity, sera were tested from 109 consecutive patients with elevated total serum amylase. Without knowledge of the isoamylase and lipase results, an assessment was made of the confidence with which the attending medical staff had made or excluded a diagnosis of acute pancreatitis. The attending staff had considered acute pancreatitis to be probable in 78, possible in 12 and unlikely in 19 patients. The confidence of the clinical diagnosis of acute pancreatitis was directly related to the degree of elevation of the serum total amylase: (mean IU/l +/- s.e.m.) probable pancreatitis 1807 +/- 313, possible pancreatitis 680 +/- 74, pancreatitis unlikely 493 +/- 50. Pancreatic isoamylase was elevated in 97% of patients with probable pancreatitis, 92% with possible pancreatitis and 68% in whom pancreatitis had been considered unlikely. Lipase elevations generally parallelled these results. Although gall-stones were usually sought among patients with probable pancreatitis, they were rarely sought in patients in the other categories. In conclusion, amylase isoenzyme or lipase determinations add little information in cases of clinically suspected acute pancreatitis with marked hyperamylasemia. The tests may have a role in the evaluation of patients with clinically unexplained hyperamylasemia by defining more precisely the origin of the amylase.