Research Associate Tufts Cummings School of Veterinary Medicine North Grafton, Massachusetts, United States
Abstract:
Background: The Wellness Ready insulin assay (WR-INS) is now available to assess insulin status in horses. An independent comparison of this assay with the radioimmunoassay for insulin (RIA-INS) is warranted.
Hypothesis: That WR-INS concentration would correlate closely with RIA-INS concentration in horses.
Animals: Twenty-four adult horses (median age 16 years) undergoing routine oral sugar testing to assess insulin status.
Methods: 144 EDTA whole blood samples were collected from horses undergoing low-dose and high-dose oral sugar tests in a companion study. WR-INS was performed immediately after sample collection; the remaining sample was centrifuged to separate plasma, which was stored at -80C until radioimmunoassay analysis at a commercial veterinary laboratory. Results were compared using Spearman correlation, Wilcoxon matched-pairs signed-rank testing; bias between methods was assessed using Bland-Altman plots.
Results: Insulin concentration for 78 samples (54%) fell within the working range of the WR-INS assay (20.0–99.9 µIU/mL). WR-INS and RIA-INS results had good correlation for these 78 samples (rs = 0.84, P < 0.001). For these time points, median insulin concentrations were significantly higher (P < 0.001) for WR-INS concentrations compared to RIA-INS concentrations. A mean bias of 17% was detected for WR-INS compared to RIA-INS concentrations. Using previously established relevant insulin thresholds for the low- and high-dose oral sugar tests, two horses (8%) had positive results using the WR-INS and negative results with the RIA-INS.
Conclusion: WR-INS concentrations are well correlated with RIA-INS results; however, the WR-INS results are significantly higher than RIA-INS, which warrants consideration when interpreting WR-INS assay results.
