Comparison of two methods for measurement of equine insulin

Diagnosis of equine hyperinsulinemia requires an accurate method for quantification of equine insulin concentrations. The objectives of the current study were to compare 2 commercially available techniques for measurement of equine insulin, the radioimmunoassay (RIA) and chemiluminescent immunoassay (CIA). Recovery was poor for both assays, but worse for the CIA. Serial dilution of a high endogenous insulin sample yielded better linearity for the RIA (r2 = 0.99, P < 0.001) than the CIA (r2 = 0.92, P = 0.009). Bland–Altman analysis indicated that the CIA was, on average, 91 pmol/l higher than the RIA, with wide limits of agreement (95% limits of agreement: –508 to 691 pmol/l). These findings suggest that results between the assays should not be considered interchangeable.