A number of studies have also suggested that amylase may be less elevated in alcohol-induced pancreatitis compared to other causes. This is due to interference with the assay by either a circulating inhibitor or the hyperlipidaemia itself. In pancreatitis due to hypertriglyceridaemia, the serum amylase can be normal in up to 50% of cases. 2, 3, 5 The sensitivity is also influenced by other factors, including the timing of the test and the cause of the pancreatitis. Most guidelines now suggest an amylase concentration 2–4 times the upper limit of normal is optimal for diagnostic accuracy, but this may reduce the sensitivity of the test to as low as 60%. However, this does depend on the definition of ‘abnormal’ and the cut-off values chosen. In studies using radiological evidence as the ‘gold standard’ for acute pancreatitis, serum amylase has a sensitivity of 81–95%. It also varies between laboratories despite attempts to adopt standardised reference methods. The reference range is typically 20–300 U/L, but does vary with age and gender. Almost all laboratories currently measure total serum amylase so the result includes both isoenzymes. It predominantly acts to digest starch, glycogen and related polysaccharides. Serum amylase is secreted in specific isoforms by the salivary glands (s-amylase) and pancreas (p-isoamylase).
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