Amylase (Blood)

Diagnostic Use

There are 2 forms of circulating amylase: P-amylase is specific for the pancreas as tissue of origin. S-amylase can originate from many organs, including salivary and parotid glands, breast, amniotic fluid, lungs, testes and fallopian tubes, as well as neoplasms (including pancreatic cancer). The amylase test measures both S and P-amylase forms thus is not very specific for pancreas pathology. P-amylase test is not a routine test but is available at LabPLUS – it needs to be specifically requested or test added within 6 days of collection.

Acute pancreatitis:

Amylase level peaks at around 48hrs and decline over 3 to 4 days. The diagnosis of acute pancreatitis should not rely solely on arbitrary limits of 3 or 4 times above upper reference limit but also on other clinical/radiological findings. Peak level amylase does not correlate with severity.

A normal amylase on presentation does not exclude acute pancreatitis especially if the patient presents very early or a few days late. Amylase can also be normal or only minimally raised in hypertriglyceridaemia related acute pancreatitis. Prolonged elevation of amylase may be due to pancreatic pseudocyst.

Non-pancreatitis causes of raised amylase include acute abdominal disorders e.g. from perforated peptic ulcer, acute cholecystitis, intestinal obstruction, trauma, ectopic pregnancy and, renal failure. Salivary gland inflammatory disorders (parotitis, mumps) or trauma can increase total amylase, with normal P-amylase.

Lipase testing supercedes amylase as the preferred marker for diagnosis of acute pancreatitis as it is more sensitive and specific.

Macro-amylasaemia is a benign cause of persistently raised amylase otherwise not well explained. It is due to complexing of amylase to large proteins with reduced renal clearance. Lipase should be normal under this circumstance. If macro-amylasaemia is suspected, contact the laboratory at ext 58519 to discuss with the on call chemical pathologist as a Polyethylene Glycol precipitation (PEG) test can be arranged. Paired testing of plasma and spot urine for amylase and creatinine allows calculation of amylase clearance which is typically low in macro-amylasaemia. However, its predictive value is not high.

Reduced amylase activity can be observed in some patients with pancreatic insufficiency or cystic fibrosis but it is not sensitive enough to be of use as a diagnostic or monitoring marker for these conditions.

Reference Intervals

28-100 U/L