Isolated elevation of aspartate aminotransferase (AST) in an asymptomatic patient due to macro-AST

A rare and benign cause of isolated aspartate aminotransferase (AST) increase is due to the presence of macro aspartate aminotransferase (macro-AST). Macro-AST is not usually considered by clinicians, leading to a large number of unnecessary and even invasive tests before diagnosed. Most commonly used laboratory methods for detection of macro-enzymes are precipitation with polyethylene glycol (PEG), ultracentrifugation and gel filtration chromatography (GFC).

We report a case of an asymptomatic patient with persistent isolated AST elevation. PEG precipitation and an alternative method based on the low stability of this macro-enzyme were performed on the patient serum.

Macro-AST was early detected by the laboratory observing a significant decrease in AST concentrations when the serum is stored at 4ºC.

Macro-AST detection based in this method can be very useful as screening, especially in those laboratories where other technologies are not available. Macro-AST must be considered as cause of unexplained isolated AST elevations before prior investigations to avoid the consequent cost and potential harm to the patient. In our case, early detection of macro-AST with this method avoided unnecessary treatment and invasive test such as liver biopsy.