Background: It is well known that both insulin resistance and insulin deficiency are involved in the pathogenesis of post-transplant diabetes mellitus (PTDM), but the relative importance of the two different mechanisms is still under debate. The present prospective longitudinal study was performed over 6 years to investigate the impact of impaired insulin secretion (ISec) and insulin sensitivity (IS) in the development of PTDM in renal transplant recipients.
Methods: A total of 95 non-diabetic patients underwent a 75 g oral glucose tolerance test (OGTT) 10 weeks post-transplant. Six years later, 63 of these recipients were re-examined, the majority (n = 58) with an OGTT. Fasting, 1- and 2-h insulin and glucose levels were measured and used to estimate the insulin secretory response and IS both at baseline and at follow-up.
Results: The proportion of recipients with normal glucose tolerance (NGT) rose from 46% (baseline) to 65% (follow-up) (P = 0.008), and median fasting and 2-h serum glucose were reduced by 0.7 mmol/l (P < 0.001) and 1.3 mmol/l (P = 0.039), respectively. The recipients with PTDM at follow-up had a significant decline in the estimated median first and second phase ISec (-58 and -47%, respectively, P = 0.005 for both). The patients who normalized their glucose tolerance from PTDM or IGT at baseline to NGT at follow-up increased their IS significantly (68%, P = 0.002) without significant alterations in ISec.
Conclusions: Impaired ISec seems to be the dominant mechanism in the development of PTDM after renal transplantation. In contrast, normalization of glucose intolerance is associated with improved IS.