SydPath

Amylase

Return to SydPath Homepage
Return to Information Sheet Page

Contents

General
High amylase concentrations in plasma
Amylase isoenzymes
Macroamylase

Structure and Function: Amylase is an enzyme produced by the exocrine glands with ability to cleave 1,4-glucose linkages. Amylase breaks down starch into maltose and limit dextrans. a -amylase is found in animals, ß-amylase in plants. The enzyme requires calcium and chloride ions for activity. There are at least 2 amylase isoenzymes, S (salivary, 1) and P (pancreatic, 2). It is a lyase (1,4-glucanglucanohydrolase). MW 45,000. EC 3.2.1.1.
Physiology: Amylase is produced in the pancreas and salivary glands and to a lesser extent the fallopian tubes. Very little is present in other organs. From the pancreas amylase is secreted via the pancreatic and then common bile ducts into the duodenum where it plays an important role in digestion of complex carbohydrates. In normal plasma about 40% of circulating amylase of pancreatic origin, the rest coming from the salivary glands.

Amylase may be released into the circulation by damage to tissues containing high levels of the enzyme, or by escape from the gastro-intestinal tract.

High levels of serum amylase may be found in:

• Acute pancreatitis - may reach very high levels, elevated in 80% of cases within 24hours
      - ususally greater than 3 times the upper reference limit
• Chronic pancreatitis – usually lower levels than acute pancreatitis
• Mumps, parotitis and other salivary gland disorders
• Perforated gastric ulcer - presumably by gastric acid causing inflammation of the pancreas
• Abdominal Aortic Aneurism (AAA)
• Intestinal obstruction – by escape from expanded bowel wall into blood stream
• Peritonitis – due to direct inflammation of the pancreas
• Tubo-ovarian abscess - from amylase in fallopian tube
• Pancreatic pseudocyst - persistently increased levels seen after attack of acute pancreatitis
• Blunt abdominal trauma
• After ERCP – may occur transiently in up to 25% of cases
• Drugs, eg morphine (close sphincter of Oddie) - increase usually <3x upper limit of normal
• Chronic alcoholism - often salivary in origin
• Diabetic keto-acidosis – does not usually indicate pancreatitis
• Macroamylasaemia (see below)
• Renal Disease – due to decreased renal excretion

Amylase is ususally measured in plasma as a test for pancreatitis. Occasionally there may be confusion over the tissue origin of a raised serum amylase when salivary gland or fallopian tubes may be implicated. Ususally the simplest way to determine the likely source is to measure a serum lipase, as this enzyme is not found in the latter two structures. If necessary the pancreatic and salivary forms of the enzyme can be identified by one of two methods. Amylase electrophoresis can determine the predominant form in plasma. This method is not quantitative but can detect Macroamylase. The levels of the two forms can be determined by immune-precipitation using a monoclinal antibody directed against salivary amylase. As each of these methods may take a week before a result is available, lipase is clearly a more useful test in most cases.

Amylase may be bound to an immunoglobulin to form macroamylase. While there is no clinical significance to the finding of a macroamylase in a patient’s plasma, it may cause some diagnostic dilemas. A persistent elevated amylase with normal plasma lipase and no other features suggestive of pancreatic, salivary or abdominal disease is suggestive of macroamylasaemia. The diagnosis is supported by finding a normal level of plasma lipase and can be confirmed by finding a normal level of urinary amylase or by amylase electrophoresis.

(top of page) 

 For further information please contact Dr Graham Jones on 8382-9100

gjones@stvincents.com.au