August 11, 2005
Diagnosis and Symptoms, Other
Question from Algoma, Wisconsin, USA:
I am a 56 year old male with type 1 diabetes. I was originally diagnosed as a type 2 and went through all five classes of oral medications with no success. I then progressed to insulin with multiple daily injections and finally have been placed on an insulin pump. When I was first diagnosed with diabetes, I had a C-Peptide of 1.9. The laboratory range was 1.1-4. My last C-Peptide was 1.0 again with the laboratory range of 1.1-4. It was then that my diagnosis was changed from type 2 to type 1. However, the GAD test was not positive but within normal range. I thought to have type 1 diabetes you needed a positive GAD test. Will I develop a positive GAD in time?
Answer:
A positive anti-GAD antibody titer is helpful in assigning a diagnosis of type 1 diabetes. However, a normal titer does not rule it out. Very often, the antibody titer can be positive at the time of diagnosis and revert to normal over time. Anti-GAD antibody appears to maintain a positive level longer than the others, but is not guaranteed to stay positive. In addition, when interpreting C peptide levels, it is important to make sure they are evaluated in light of the simultaneous glucose reading. For instance, a low C-peptide level at a time you are hypoglycemic is appropriate, compared to when you are hyperglycemic.
JTL