Islet cell function in type 1 and type 2 diabetes

The primary hormone controlling glucose metabolism is insulin. A deficiency in insulin secretion is a central defect in the pathophysiology of both type 1 and type 2 diabetes. In this review we discuss the abnormalities of insulin secretion characteristic of both forms of diabetes. We describe most of the commonly employed tests of beta cell function and explore their relative advantages and disadvantages. Usually, there is a trade-off between the complexity of the test and the amount of information obtained. For example, measuring insulin or C-peptide during the fasting state provides far less information on total beta cell functional capacity than does dynamic beta cell testing at different glucose levels using several intravenous beta cell secretagogues. Since insulin and C-peptide are the primary measurements used during beta cell testing, a few caveats are provided regarding both of these assays and the interpretation of results.