In Diabetic ketoacidosis when pain abdomen is one of the major clinical finding, serum amylase levels are obtained, to rule out the diagnosis of acute pancreatitis (since the latter too can present with acute pain abdomen).
If the serum amylase levels are found high in patients with Diabetic ketoacidosis, it may not be due to acute pancreatitis. In Diabetic ketoacidosis amylase levels rise because of the amylase that originates from the saliva, rather from the pancreas.
However, the diagnosis of acute pancreatitis should be excluded. And to do that a serum lipase levels should be ordered. If both serum amylase and lipase are raised, the diagnosis bends more towards acute pancreatitis. So a serum lipase level can be helpful in such a clinical scenario.