title: Laboratory detection of macro-aspartate aminotransferase: case report and evaluation of the PEG-precipitation method.
abstract: BACKGROUND
  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).
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  Early recognition of macro-AST, proven by simple PEG precipitation, can avoid time-consuming and invasive investigations.
authors.affiliation: ZNA Clinical Laboratory, campus Middelheim, Lindendreef 1, Antwerp, Belgium. lisbeth.patteet@ua.ac.be
authors.forename: Lisbeth
authors.initials: L
authors.lastname: Patteet
authors.forename: Marc
authors.initials: M
authors.lastname: Simoens
authors.forename: Marian
authors.initials: M
authors.lastname: Piqueur
authors.forename: Annick
authors.initials: A
authors.lastname: Wauters
mesh_terms: D000328:Adult; D001219:Aspartate Aminotransferases / Q000097:blood*; D002498:Centrifugation; D011232:Chemical Precipitation; D005260:Female; D006801:Humans; D011092:Polyethylene Glycols
chemical_list: D011092:Polyethylene Glycols; D001219:Aspartate Aminotransferases