title: Evaluation of a commercially available radioimmunoassay and species-specific ELISAs for measurement of high concentrations of insulin in equine serum.
abstract: OBJECTIVE
  To evaluate a human radioimmunoassay (RIA) and equine and high-range porcine (hrp) species-specific ELISAs for the measurement of high serum insulin concentrations in ponies.
  
  
  METHODS
  Serum samples from 12 healthy nonobese ponies (7 clinically normal and 5 laminitis prone; 13 to 26 years of age; 11 mares and 1 gelding) before and after glucose, insulin, and dexamethasone administration.
  
  
  METHODS
  Intra-and interassay repeatability, freeze-thaw stability, dilutional parallelism, and assay agreement were assessed.
  
  
  RESULTS
  Assay detection limits were as follows: RIA, < 389 μU/mL; equine ELISA, < 175 μU/mL; and hrp ELISA, 293 to 8,775 μU/mL. Mean ± SD intra- and interassay repeatability were respectively as follows: RIA, 6.5 ± 5.1 % and 74 ± 3.4%; equine ELISA, 10.6 ± 11.0% and 9.0 ± 4.6%; and hrp ELISA, 19.9 ± 172% and 173 ± 16.6%. Freezing and thawing affected measured concentrations. Dilutional parallelism in the RIA was only evident when insulin-depleted equine serum was used as a diluent (percentage recovery, 95.7 ± 274%); in the ELISAs, dilutional parallelism was observed when a zero calibrator was used. Agreement between RIA and equine ELISA results was good for samples containing concentrations < 175 μU of insulin/mL (bias, -18.5 ± 25.5 μU/mL; higher in RIA). At higher concentrations, assay agreement was poor between RIA and equine ELISA results (bias, -185.3 ± 98.7 μU/mL) and between RIA and hrp ELISA results (bias, 25.3 ± 183.0 μU/mL).
  
  
  CONCLUSIONS
  Agreement among results of the 3 assays was variable, and dilutional parallelism was only evident with the RIA when insulin-depleted equine serum was tested. Caution is recommended when evaluating high insulin concentrations measured with the RIA or ELISAs.
authors.affiliation: Department of Veterinary Clinical Sciences, Royal Veterinary College, North Mymms, Hatfield, Hertfordshire, AL9 7TA, England. kborer@rvc.ac.uk
authors.forename: Kate E
authors.initials: KE
authors.lastname: Borer-Weir
authors.forename: Simon R
authors.initials: SR
authors.lastname: Bailey
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Menzies-Gow
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Harris
authors.forename: Jonathan
authors.initials: J
authors.lastname: Elliott
mesh_terms: D000818:Animals; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods* / Q000662:veterinary; D005260:Female; D006736:Horses / Q000097:blood*; D006801:Humans; D007328:Insulin / Q000097:blood*; D057230:Limit of Detection; D008297:Male; D011863:Radioimmunoassay / Q000379:methods* / Q000662:veterinary; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013045:Species Specificity; D013552:Swine / Q000378:metabolism*
chemical_list: D007328:Insulin