Our patient was diagnosis and treated as CFRD for many years primarily on the basis of a positive c-peptide measured soon after her initial presentation,as well as due to the historical transmission of such diagnosis through the various institutions where she was treated. Interestingly,our patient's c-peptide became undetectable 4 years after her initial
diagnosis, which is more consistent with type 1 diabetes as are her rapid progression from normal glucose tolerance to mild DKA in absence of CF exacerbation and initially normal pancreatic exocrine function. However, Kessler and colleagues have reported that baseline
c-peptide levels in CFRD patients many may be undetectable even in patients with negative
GAD antibodies. In addition, CF patients have been shown to have a blunted response to hyperglycemia based on their c-peptide in Moran et al.'s paper.