Optimising the Siemens Coat-A-Count Radioimmunoassay to Measure Insulin in Equine Plasma

As insulin resistant horses risk laminitis,1 accurate measurement of plasma insulin concentrations is important. The Siemens Coat-A-Count Insulin Radioimmunoassay (RIA) (Siemens Medical Solutions Diagnostics, Los Angeles, CA) is widely used to quantify insulin in equine plasma. This assay is optimised to detect human insulin, with an anti-human insulin antibody, but there is good reason to anticipate cross-reactivity based on the highly conserved nature of insulin among mammalian species.2 We evaluated this assay due to concerns that the RIA did not measure equine insulin accurately when high concentrations were determined through dilution.