title: Comparison of competitive radioimmunoassays and two-site sandwich assays for the measurement and interpretation of plasma ghrelin levels.
abstract: BACKGROUND
  Ghrelin, an endogenous ligand for the GH secretagogue receptor, is an orexigenic peptide hormone produced primarily by the stomach. Recent studies suggest significant differences in the specificity of currently available ghrelin assays.
  
  
  OBJECTIVE
  The aim of the study was to compare four ghrelin assays (two commercially available and two developed by our group) of differing specificity, each used on the same set of more than 800 plasma samples from a human study.
  
  
  METHODS
  Thirteen volunteers were sampled every 20 min for 6 h after consumption of one of three isocaloric drinks consisting of either 80% fat, 80% carbohydrate, or 80% protein. The samples were assayed by RIA for total and active ghrelin, as well as by sandwich assays for acyl and des-acyl ghrelin. The ghrelin profiles for each individual were smoothed using a statistical algorithm to lessen the effects of pulsatility and noise.
  
  
  RESULTS
  The sandwich assays for acyl and des-acyl ghrelin yielded ghrelin values that were lower than those from the corresponding RIAs. The ghrelin profiles after nutrient ingestion were similar, yet key differences among the four assays were apparent; in particular, percentage changes were significantly greater in the sandwich assays.
  
  
  CONCLUSIONS
  The lower levels and greater relative changes in ghrelin values reported by the sandwich assays are consistent with greater assay specificity. When applied to the nutrient study, the sandwich assays were better able to distinguish the different responses to different nutrients than were the RIAs.
authors.affiliation: Department of Chemistry, University of Virginia, Charlottesville, Virginia 22908, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Prudom
authors.forename: Jianhua
authors.initials: J
authors.lastname: Liu
authors.forename: James
authors.initials: J
authors.lastname: Patrie
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Gaylinn
authors.forename: Karen E
authors.initials: KE
authors.lastname: Foster-Schubert
authors.forename: David E
authors.initials: DE
authors.lastname: Cummings
authors.forename: Michael O
authors.initials: MO
authors.lastname: Thorner
authors.forename: H Mario
authors.initials: HM
authors.lastname: Geysen
mesh_terms: D001628:Beverages; D002149:Energy Intake; D004797:Enzyme-Linked Immunosorbent Assay; D054439:Ghrelin / Q000097:blood* / Q000276:immunology; D006801:Humans; D007202:Indicators and Reagents; D011863:Radioimmunoassay / Q000379:methods; D012680:Sensitivity and Specificity
chemical_list: D054439:Ghrelin; D007202:Indicators and Reagents