Clinical Skills Pearl Vol 2 (#12): Should I order an amylase or a lipase?

What is a better test for diagnosing pancreatitis...lipase or amylase?

Lipase is produced primarily in the pancreas, with a small amount in the liver, intestine, tongue, and stomach. Amylase is derived primarily from the pancreas and salivary glands; it is also present in the ovaries, small and large intestine, and skeletal muscle. Serum amylase is the most commonly used lab test. Serum lipase is believed to be more specific and will stay elevated for a longer period of time, as hyperlipasemia persists for 7 days and amylase should normalize within 4 days. Becuase lipase stays higher longer it may be more sensitive. However it is agreed that patients should be followed on their clincial improvement not on an absolute value of amylase or lipase.

Normal serum amylase and lipase levels do not exclude acute pancreatitis. In one consecutive series, normal serum amylase was documented in 67 of 352 (19%) of contrast–enhanced CT-proven cases of acute pancreatitis.

What other entities could cause an elevated amylase or lipase?

Disease can occur in other organs that produce amylase/lipase. Transmural absorption in intestinal infarction and transperitoneal absorption with a perforated viscus and peritonitis probably explain the hyperamylasemia/hyperlipasemia in these conditions. There is decreased renal clearance in patients with renal failure. Macroamylasemia is a condition in which amylase is bound to a larger protein moiety that prevents renal excretion. Thus, serum amylase is elevated in absence of pancreatitis. Macroamylasemia is diagnosed by detecting a low renal amylase clearance. Increased amylase and lipase
in cholecystitis is probably due to subclinical or undiagnosed coexistent pancreatitis.

Amylase levels may also be significantly increased in patients with pancreatic duct obstruction, cancer of the pancreas, and gallbladder attacks. Urine and blood amylase levels may also be elevated with a variety of other conditions, such as ovarian cancer, lung cancer, tubal pregnancy, mumps, intestinal obstruction, or perforated ulcer, but amylase tests are not generally used to diagnose or monitor these disorders. Decreased blood and urine amylase levels may indicate permanent damage to the amylase-producing cells in the pancreas. Increased blood amylase levels with normal to low urine amylase levels
may indicate decreased kidney function or the presence of a macroamylase, a benign complex of amylase and other proteins that accumulates in the blood.

Dr. Maynard Luterman

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