the oral sugar test also requires giving the horse only a single flake of hay at 10pm the night before the test. the following morning, karo corn syrup is given orally, and glucose and insulin levels are measured at 60 and 90 minutes after administration. normal or excessively high insulin levels are diagnostic. however, equivocal test results require retesting at a later date, or performing a different test. a similar test is available outside the us, in areas where corn-syrup products are less readily available, where horses are given a morning meal of chaff with dextrose powder, and blood insulin levels are measured 2 hours later.