title: Specificity and sensitivity of commercially available assays for glucagon-like peptide-1 (GLP-1): implications for GLP-1 measurements in clinical studies.
abstract: OBJECTIVE
  To evaluate the performances of commercially available glucagon-like peptide-1 (GLP-1) assays and the implications for clinical studies.
  
  
  METHODS
  Known concentrations (5-300 pmol/l) of synthetic GLP-1 isoforms (GLP-1 1-36NH2, 7-36NH2, 9-36NH2, 1-37, 7-37 and 9-37) were added to the matrix (assay buffer) supplied with 10 different kits and to human plasma, and recoveries were determined. Assays yielding meaningful results were analysed for precision and sensitivity by repeated analysis and ability to discriminate low concentrations. Endogenous GLP-1 levels in clinical samples were assessed using three commercial kits.
  
  
  RESULTS
  The USCN LIFE assay detected none of the GLP-1 isoforms. The active GLP-1 enzyme-linked immunosorbent assays (ELISAs) from Millipore and DRG appeared identical and were specific for intact GLP-1 in buffer and plasma. The Meso Scale Discovery (MSD) total GLP-1 kit detected all six GLP-1 isoforms, although recovery of non-active forms was incomplete, especially in plasma. Millipore total GLP-1 ELISA kit detected all isoforms in buffer, but mainly amidated forms in plasma. The Alpco, Phoenix and Bio-Rad kits detected only amidated GLP-1, but the Alpco kit had a limited measurement range (30 pmol/l), the Phoenix kit had incomplete recovery in plasma and the Bio-Rad kit was insensitive (detection limit in plasma 40 pmol/l). The pattern of postprandial GLP-1 responses in clinical samples was similar between the kits tested, but the absolute concentrations measured varied.
  
  
  CONCLUSIONS
  The specificity and sensitivity of commercially available kits for the analysis of GLP-1 levels vary considerably. This should be taken into account when selecting which assay to use and when comparing data from different studies.
authors.affiliation: NNF Center for Basic Metabolic Research, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark; Department of Human Nutrition, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: M J
authors.initials: MJ
authors.lastname: Bak
authors.forename: N J
authors.initials: NJ
authors.lastname: Wewer Albrechtsen
authors.forename: J
authors.initials: J
authors.lastname: Pedersen
authors.forename: F K
authors.initials: FK
authors.lastname: Knop
authors.forename: T
authors.initials: T
authors.lastname: Vilsbøll
authors.forename: N B
authors.initials: NB
authors.lastname: Jørgensen
authors.forename: B
authors.initials: B
authors.lastname: Hartmann
authors.forename: C F
authors.initials: CF
authors.lastname: Deacon
authors.forename: L O
authors.initials: LO
authors.lastname: Dragsted
authors.forename: J J
authors.initials: JJ
authors.lastname: Holst
mesh_terms: D000595:Amino Acid Sequence; D004797:Enzyme-Linked Immunosorbent Assay; D005934:Glucagon / Q000737:chemistry* / Q000276:immunology; D052216:Glucagon-Like Peptide 1 / Q000032:analysis* / Q000276:immunology; D006801:Humans; D010446:Peptide Fragments / Q000097:blood*; D011863:Radioimmunoassay; D012680:Sensitivity and Specificity
chemical_list: D010446:Peptide Fragments; D052216:Glucagon-Like Peptide 1; D005934:Glucagon
keywords: cross-reactivity; enzyme-linked immunosorbent assay; glucagon-like peptide-1; precision; radioimmunoassay; sensitivity; specificity