Background: Persistent isolated elevation of aspartate aminotransferase (AST) is a rare observation and might lead to unnecessary laboratory testing and invasive procedures, if the possibility of macro-AST is not considered.
Methods: We report the case of a healthy 28-year-old female patient with persistent isolated elevation of AST. In order to confirm the suspected diagnosis of macro-AST, polyethylene glycol (PEG) precipitation and repeated measurements of enzyme activity after refrigeration at 2 - 8°C were performed.
Results: PEG precipitation confirmed the presence of macro-AST, while repeated measurements after refrigeration did not show any relevant decrease in enzyme activity.
Conclusions: Especially in clinically asymptomatic patients, macro-AST must be considered as a cause of persistent isolated elevations in AST activity to avoid costly and potentially harmful medical tests or procedures. PEG precipitation is a feasible and cost-effective way to establish the diagnosis, while repeated measurement of enzyme activity after refrigeration potentially leads to wrong conclusions.