Beta cell function (revision 1)

Beta cell function is the capacity of the pancreatic beta cell to secrete insulin in amounts appropriate to the prevailing glucose concentration and to the prevailing insulin sensitivity. It is not a single quantity and cannot be measured directly in a living person; every clinical measure is an inference from insulin or C-peptide concentrations under some defined stimulus.^[1]

The central methodological difficulty is that secretion and sensitivity are not independent. A healthy beta cell compensates for insulin resistance by secreting more, so an absolute secretion figure that looks normal may represent substantial dysfunction in a very insulin-resistant person. Measures that do not adjust for sensitivity — including fasting insulin and HOMA-B — are therefore weak, and the disposition index, the product of a secretion measure and a sensitivity measure, was devised to address exactly this.^[2]