Comparison of metabolic responses to the mixed meal tolerance test vs the oral glucose tolerance test after successful clinical islet transplantation

Following islet transplantation, mixed meal tolerance tests ( MMT s) are routinely utilized to assess graft function, but how the 90‐minute MMTT glucose value relates to a 120‐minute glucose concentration of ≥11.1 mmol/L used to diagnose diabetes following a standardized 75 g‐ OGTT , is not known. We examined this relationship further. Thirteen subjects with Type 1 diabetes and stable transplant grafts, not on exogenous insulin with HbA1c < 7% (53 mmol/mol), were studied on 17 occasions with paired OGTT s and MMTT s. Receiver operating characteristic ( ROC ) curves were constructed to derive the 90‐minute MMTT glucose threshold associated with a 120‐minute glucose concentration following a 75 g‐ OGTT ( OGTT 120 ) ≥11.1 mmol/L and their diagnostic accuracy. Studies with OGTT 120 ≥11.1 mmol/L (n = 5) had diminished C‐peptide: glucose, greater integrated glucose and diminished insulin: glucose area under the curve ( AUC ) ratios (0‐120 minutes) and disposition indices; all P  < .05, contrasting with MMTT s where no difference in the 90‐minute glucose concentrations, C‐peptide:glucose, integrated glucose, C‐peptide and C‐peptide: glucose AUC s (0‐90 minutes) was seen; all P  > .05. A 90‐minute MMTT glucose concentration ≥8.0 mmol/L demonstrated a sensitivity and specificity of ≥80% for the diagnosis of OGTT 120 ≥11.1 mmol/L; area under ROC curve (mean ±  SEM ) 73 ± 13%. A 90‐minute MMTT glucose ≥8.0 mmol/L, identifies islet transplant recipients who may require closer monitoring for graft dysfunction.