Serum amylase

A 38-year-old woman who is hypotensive and has severe abdominal pain requires

review. She has a raised serum amylase. Which of the following is the LEAST LIKELY

to explain her symptoms and biochemical findings?

a) Perforated duodenal ulcer

b) Ruptured ectopic pregnancy

c) Diabetic ketoacidosis

d) Myocardial infarction

e) Acute pyelonephritis

Answer: e

Explanation

Amylase is a digestive enzyme that usually acts extracellularly to cleave starch into

monosaccharides by hydrolysis of internal alpha-1,4-glycoside bonds resulting in the

production of maltose and oligosaccharides. A variety of organs and secretions contain

amylase activity, including the pancreas, salivary glands, fallopian tubes and cyst

fluid, testes, lungs, thyroid, tonsils, breast milk, sweat, tears and some malignant

neoplasms (e.g. myeloma, phaeochromocytoma and carcinoma of the breast). The

first two organs account for over 90% of the amylase produced. Electrophoresis

shows that serum amylase is of two main types, P-type amylase from the pancreas,

and S-type amylase from the salivary glands. Patients with acute pancreatitis usually

have a raised amylase level but it may be normal even in the most severe cases of

pancreatic necrosis and raised in many other conditions hence the use of serum lipase

as a diagnostic test for acute pancreatitis. Other intra-abdominal pathologies causing

raised amylase levels include inflammatory disease of the small intestine, mesenteric

infarction, intestinal obstruction, appendicitis, abdominal aortic aneurysm and peritonitis,

all of which usually result in increased P-type isoamylase. Serum amylase levels

will also be raised in patients with liver and renal failure due to decreased clearance.

Ruptured ectopic pregnancy, myocardial infarction and diabetic ketoacidosis are

among other, non-GI tract causes of raised serum amylase level but not acute

pyelonephritis.