Fasting parameters for estimation of stimulated β cell function in islet transplant recipients with or without basal insulin treatment

In order to assess beta cell secretory capacity after islet transplantation, standardized mixed meal stimulation tests are often used. But these tests are cumbersome and the effect of exogenous insulin on the test results is unclear. The aim of our study was to determine to what extent fasting glycemic indices can estimate stimulated beta cell function in islet transplant recipients with and without basal insulin. In total 100 mixed meal stimulation tests, including 31 with concurrent basal insulin treatment, were performed in 36 islet transplant recipients. In a multivariate model, fasting C-peptide and fasting glucose together estimated peak C-peptide withR(2) = .87 and area under the curve (AUC) C-peptide with aR(2) = .93. There was a larger increase of glucose during tests in which exogenous insulin was used (+7.9 vs +5.3 mmol/L,P < .001) and exogenous insulin use was associated with a slightly lower estimated peak C-peptide (relative change: -15%,P = .02). In islet transplant recipients the combination of fasting C-peptide and glucose can be used to accurately estimate stimulated beta cell function after a mixed meal stimulation test, whether exogenous basal insulin is present or not. These data indicate that graft function can be reliably determined during exogenous insulin treatment and that regular islet graft stimulation tests can be minimized.

Automated summary

The study found that fasting C-peptide and glucose levels can accurately estimate stimulated beta cell function after islet transplantation, regardless of the presence of exogenous basal insulin. Tests with exogenous insulin showed a larger increase in glucose levels, and exogenous insulin use was associated with a slightly lower estimated peak C-peptide. This suggests that graft function can be reliably determined during exogenous insulin treatment, potentially minimizing the need for regular islet graft stimulation tests.