Macroamylasemia 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-polymerize and/or form immune complexes with immunoglobulins.
Macroamylasemia is found in ~1% normoamylasaemic individuals and up to 2.5% in those with hyperamylasemia 4. It has been found more commonly in men and the middle-aged but this is based on limited datasets.
Macroenzymes are not uncommon on laboratory assays of human blood. Many proteins self-polymerize 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 macroamylasemia 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 macroamylasemia the molecule is too large to be filtered by the kidney resulting in a normal urinary amylase despite an elevated serum amylase 3.
This condition can be confused with other causes of raised serum amylase (e.g. acute pancreatitis). Macroamylasemia 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 macroamylasemia
- liver disease
- diabetes mellitus
- autoimmune disorders
- infusion of hydroxyethyl starch (HES)
History and etymology
Macroamylasemia was first described in 1964 by Wilding. The term 'macroamylasemia' was coined by Berk et al. in 1967 4.