title: Detection of macro-creatine kinase and macroamylase by polyethylene glycol precipitation and ultrafiltration methods.
abstract: BACKGROUND
  Macroenzymes may cause elevations in serum enzyme activity. Macroenzymes are not common; however their detection is important because they cause diagnostic confusion and therapeutic errors.
  
  
  METHODS
  We analyzed 2 of the most prevalent macroenzymes in the literature, macro-creatine kinase (macro-CK) and macroamylase, using 2 methods for detection, polyethylene glycol (PEG) precipitation and ultrafiltration (UF). Enzyme measurements were made using a Roche Modular Analytics P analyzer. Imprecision was assessed using quality control material. We evaluated 125 samples from apparently healthy subjects to establish reference intervals. For macro-CK comparison, 94 samples with activities >200 U/l were analyzed with both PEG precipitation and UF and compared to electrophoresis. PEG precipitation and UF were compared for macroamylase detection using 130 samples with amylase activities >110 U/l.
  
  
  RESULTS
  UF was more precise and demonstrated narrower reference intervals for both analytes. PEG precipitation and UF were able to detect true cases of macro-CK with overall agreement with electrophoresis of 79.8% and 80.9%, respectively. Both methods detected the same number of 'positive' macroamylase samples; however PEG precipitation resulted in a greater number of 'indeterminate' cases.
  
  
  CONCLUSIONS
  This is the first report where UF has been shown useful for the detection of both macro-CK and macroamylase.
authors.affiliation: ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT 84108, USA.
authors.forename: Sara P
authors.initials: SP
authors.lastname: Wyness
authors.forename: Joshua J H
authors.initials: JJ
authors.lastname: Hunsaker
authors.forename: Sonia L
authors.initials: SL
authors.lastname: La'ulu
authors.forename: Lokinendi V
authors.initials: LV
authors.lastname: Rao
authors.forename: William L
authors.initials: WL
authors.lastname: Roberts
mesh_terms: D000328:Adult; D000681:Amylases / Q000097:blood*; D011232:Chemical Precipitation; D003402:Creatine Kinase / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011092:Polyethylene Glycols / Q000737:chemistry*; D015203:Reproducibility of Results; D014462:Ultrafiltration / Q000379:methods*
chemical_list: D011092:Polyethylene Glycols; D003402:Creatine Kinase; D000681:Amylases; C001663:macroamylase