Background It may be difficult to distinguish between adults
with type 1 diabetes and type 2 diabetes by clinical assessment.
In patients undergoing bariatric surgery, it is critical to
correctly classify diabetes subtype to prevent adverse perioperative
outcomes including diabetic ketoacidosis. This study
aimed to determine whether testing for C-peptide and islet cell
antibodies during preoperative evaluation for bariatric surgery
could improve the classification of type 1 versus type 2 diabetes
compared to clinical assessment alone.
Methods This is a retrospective analysis of the Improving
Diabetes through Lifestyle and Surgery trial, which randomized
patients with clinically diagnosed type 2 diabetes and BMI 30–
40 kg/m2 to medical weight loss or bariatric surgery; one participant
was discovered to have type 1 diabetes after experiencing
postoperative diabetic ketoacidosis. Using blood samples collected
prior to study interventions, we measured islet cell antibodies
and fasting/meal-stimulated C-peptide in all participants.
Results The participant with type 1 diabetes was similar to
the 11 participants with type 2 diabetes in age at diagnosis,
adiposity, and glycemic control but had the lowest Cpeptide
levels. Among insulin-treated participants, fasting
and stimulated C-peptide correlated strongly with the Cpeptide
area-under-the-curve on mixed meal tolerance
testing (R = 0.86 and 0.88, respectively). Three participants,
including the one with type 1 diabetes, were islet
cell antibody positive.
Conclusions Clinical characteristics did not correctly identify
type 1 diabetes in this study. Preoperative C-peptide testing
may improve diabetes classification in patients undergoing
bariatric surgery; further research is needed to define the optimal
C-peptide thresholds