I am 52 years old. I was just diagnosed with type 1 diabetes, and got my test results to determine if I have type�1 or type�2 My C-peptide was 1.4 (Normal: 0.5-2.60), and my GAD-65 AB was 108.2. Everything else is normal (kidneys, thyroid and liver, blood pressure). Do these results indicate I have type 1 or type 2 diabetes?

Your questions are good ones. These tests are being performed more frequently as we learn more about the development of diabetes.

Blood tests for C-peptide are best evaluated with a simultaneous glucose level. For instance, if the glucose is very high and the C-peptide is in the lower end of normal, the C-peptide level is likely to be inappropriately low. If the glucose and C-peptide levels are both low, the C-peptide level may be appropriate. C-peptide is a portion of the precursor molecule of glucose. It is cleaved off when insulin is secreted from the beta cells. One molecule of C-peptide is secreted for every molecule of insulin secreted. Getting back to your question, your C-peptide is in the mid-normal range. I imagine this is for a fasting level. If your blood sugar was high at the time this was drawn, the C-peptide is not high enough. However, if the glucose was normal, the C-peptide level does not suggest type 1 diabetes. In any event, you make insulin. The question is it enough.

The GAD65 antibody titer is probably high, although you will have to ask your physician for the normal range of the lab where your test was performed. If the antibody level is high, I would put this together as suggesting you have a form of type 1 diabetes that is expressing itself later in life. If positive, I would expect your C-peptide level to drop over time. This would be suggestive of a form of diabetes referred to as Late-onset Autoimmune Diabetes of Adulthood (LADA) which eventually has to be treated with insulin.

JTL