Amylase, found mainly in pancreas and salivary glands, is used in the differentiation of acute pancreatitis from other causes of the acute abdomen.
In acute pancreatitis, amylase typically rises above 400 U/L, returning to normal in about 4 days. The enzyme pattern is inconsistent, however, and failure to detect an elevation does not preclude the diagnosis even when there is severe infarction.
Acute peritonitis, causing inflammation of the serosal surfaces of the pancreas and other organs, can elevate amylase but usually not above 400 U/L.
Other causes of hyperamylasaemia include mumps, diabetic ketoacidosis, biliary tract disease, renal insufficiency, shock, some drugs (particularly narcotics), hypoxia, pelvic infection, macroamylasaemia.
Chronic pancreatitis does not raise amylase except sometimes during acute exacerbations.
In macroamylasaemia, as in other macromolecular enzyme variants, a consistently elevated enzyme level is found in a well person.
A definitive diagnosis can be made using the amylase/creatinine clearance ratio, ACCR.
ur amylase X s creatinine
ACCR (%)= ——————————————X 100
s amylase X ur creatinine
In macroamylasaemia, the ACCR is <2%. The usual reference range is 2-5%.
What is the sensitivity and specificity of lipase in acute pancreatitis (AP)?
When the cutt-off levels of amylase were set at the upper normal level or up to 5-fold as high, the sensitivity decreased from 92% to 74%, the specificity increased from 85% to 99%. Lipase sensitivity is similar but the specificity is lower. Although once considered to be specific for AP, nonspecific elevations of lipase have been reported in almost as many disorders as amylase, thus decreasing its specificity. Simultaneous estimation of amylase and lipase does not improve the accuracy.
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