Macroamylasaemia is the presence of serum amylase of a large molecular size, seen in both otherwise healthy individuals, and also in various diseases. Amylase seems to be able to self-polymerise and/or form complexes with other blood proteins, e.g. immunoglobulins.
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Epidemiology
Macroamylasaemia is found in ~1% normoamylasaemic individuals and up to 2.5% in those with hyperamylasaemia 4. It has been found more commonly in men and the middle-aged but this is based on limited datasets.
Pathology
Macroenzymes are not uncommon on laboratory assays of human blood. Many proteins self-polymerise or form complexes with other proteins, which are normal constituents of blood, e.g. globulins, carrier molecules, etc 5.
The normal amylase molecule has a molecular weight of 45 kDa, but in macroamylasaemia the amylase forms a complex with globulin forming a much larger macromolecule ~200 kDa. Normal non-complexed amylase is freely filtered at the renal glomerulus and although most is reabsorbed in the tubules ~25% is excreted in the urine. However, in macroamylasaemia the molecule is too large to be filtered by the kidney resulting in a normal urinary amylase despite an elevated serum amylase 3.
Interpretation
This condition can be confused with other causes of raised serum amylase (e.g. acute pancreatitis). Macroamylasaemia is accompanied by normal serum lipase and urinary amylase levels. By contradistinction, in pancreatic disease the serum lipase will usually be elevated as well 2.
Causes of macroamylasaemia
- liver disease
- diabetes mellitus
- malignancy
- malabsorption
- autoimmune disorders
- infusion of hydroxyethyl starch (HES)
History and etymology
Macroamylase was first described in 1964 by Wilding. The term 'macroamylasaemia' was coined by Berk et al. in 1967 4.
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