Macroamylase

What is macroamylase?

Macroamylase is an immunoglobulin-amylase complex that forms in the circulation and cannot be adequately cleared by the kidneys. This causes benign increases in amylase concentrations. It is estimated that this affects 1-2% of the population. The causes are unclear but there is an association with autoimmune conditions, chronic liver disease and some medications.

When should I suspect a patient has macroamylase?

Typically amylase concentrations remain fairly stable in a patient with macroamylase. Unchanging raised amylase results that are inconsistent with the clinical picture should raise the suspicion of macroamylase.

How can I investigate for macroamylase?

There is no easily available test for macroamylase. If you wish to exclude a pancreatic pathology request a lipase on a serum (brown topped) sample. This is sent to an external laboratory and a result will not be available for several days. A normal lipase result with a corresponding raised amylase would be suggestive of macroamylase or a raised salivary amylase. Increases in salivary amylase are typically associated with salivary disease (eg mumps), ectopic pregnancy, lung disease, tumours and alcohol abuse. Anorexia, particularly when associated with vomiting has also been seen to increase salivary amylase.

Paired urine and serum amylase can be a useful tool to determine the likelihood of macroamylase. High levels of amylase in the blood are secondary to reduced clearance rather than excessive production and consequently serum amylase is high and urine amylase is low, leading to a low amylase clearance. The following clearance calculation can be used, with a clearance of <1% being highly suggestive of macroamylase and >5% effectively excluding it.

Urine amylase x Serum creatinine (mmol/L)  x100%

Serum amylase x Urine creatinine

There are no UK labs currently measuring macroamylase or salivary amylase directly.