Amylase

Amylase is widely employed as a marker of acute pancreatitis and a significant elevation is diagnostic.

Physiology

α-amylase is a digestive enzyme that is predominantly secreted by the acinar cells of the exocrine pancreas. It is also secreted by the salivary glands. Pancreatic amylase is encoded by AMY2, and salivary amylase by AMY1, both genes on chromosome 1 .

The main function of the amylases is to initiate the digestion of complex polysaccharides, primarily starch, to their constituent simple sugars. This starts in the mouth with salivary α-amylase, which continues to work in the stomach (it is chemically protected from the gastric acid). In the small bowel, starting in the duodenum, pancreatic α-amylase digests the dietary carbohydrate, aided by remnant salivary α-amylase .

Starch is mainly composed of two glucose polymers: amylopectin (75%) and amylose (25%), and the main action of amylase is to break their internal α1,4 linkages. This results in the formation of oligosaccharides, which are primarily maltose, maltotriose, and α-limit dextrins .

Interpretation

The salivary glands and the pancreas account for most of the normal serum amylase found in a well individual . These two amylase isoforms can be distinguished by laboratory assay. Normal serum amylase reference range is 19-86 units/liter.

Compared to lipase, the other enzyme measured in suspected cases of acute pancreatitis, amylase has poorer sensitivity and is elevated for a shorter window of time . For this reason lipase is the preferred test for acute pancreatitis.

Causes of hyperamylasemia

Amylase is found in small bowel intraluminal fluid and therefore bowel stasis can lead to abnormal absorption of the enzyme.

• pancreatitis
• other pancreatic assaults
  • ERCP/EUS: instrumentation of the main pancreatic duct
  • pancreatic trauma
  • pancreatic carcinoma
• bowel disease
  • bowel ischemia/infarction
  • bowel perforation
  • intestinal obstruction
• salivary gland pathology e.g. tumors
• reduced homeostatic removal of amylase
  • renal failure
  • macroamylasemia
• chronic alcoholism
• post-surgical
  • especially following coronary arterial bypass grafting (CABG)
• lactic acidosis
• eating disorders
  • anorexia nervosa
  • bulimia
• ectopic amylase secretion by cancer
• Gullo syndrome
• COVID-19 

Causes of hypoamylasaemia

Hypoamylasaemia was seen in 5% of samples tested for amylase over a one-year period in a recently-published study from a large academic center in London in the UK .

• functionally-absent pancreas
  • main cause of a low serum amylase is chronic pancreatitis
  • post-pancreatectomy
  • severe pancreatic trauma: chronic; acute tends to result in elevated amylase (see above)
  • cystic fibrosis
• end-stage liver disease
• genetic (very rare)
  • isolated pancreatic amylase deficiencies have been seen in a few families/individuals
  • signs and symptoms of carbohydrate malabsorption are present