Laboratory detection of macro-aspartate aminotransferase: Case report and evaluation of the PEG-precipitation method

Abstract

Chronic elevated AST without other signs of liver disease, cardiac or skeletal abnormalities, is suggestive for macro-AST. Laboratory detection can be performed by gel filtration chromatography, ultrafiltration or precipitation with polyethylene glycol (PEG). A healthy 27 year-old female was referred because of chronic elevated AST (116-704U/L) without other abnormalities. Macro-AST positivity was suspected since AST was no longer measurable in the supernatant of a serum sample (<3U/L) after PEG precipitation. Optimization of this method included analysis of proteins and lipids precipitated, testing the effect of different PEG concentrations and centrifugation times. 25% (m/v) PEG solution gave the most reliable results. No significant difference was seen between 10 and 30 min centrifugation time. A reference range was obtained by analysis of 31 normal patient samples (mean % PEG precipitation activity 35.1% with 95% confidence limits of 14.5-62.5%). Retrospective analysis of 1371 patient samples with elevated AST revealed one other positive patient sample. Early recognition of macro-AST, proven by simple PEG precipitation, can avoid time-consuming and invasive investigations.