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August 7, 2001

Blood Tests and Insulin Injections

Question from Davenport, Iowa, USA:

Two years ago, I was diagnosed with diabetes and have been on an insulin pump (getting approximately 25-30 units a day) for a little over a year, and my problem is that my medical team still isn't sure what type of diabetes I have. At the time of diagnosis, my C-peptide was 2.0 (normal values are (0.9-3.9) and my GAD65 was 0.0 ( normal values are (<= 0.02). The comments with the GAD results suggested pre-disposition to type 1 diabetes, but my doctor reported that the test was negative. With this result negative or what?


Without a few more clinical details such as your age and weight and what your insulin requirements were at the beginning, it’s difficult to make very precise suggestions. To begin with though, I would agree that your anti GAD test was negative: it is possible though that if you had also had an islet cell antibody (ICA512) and an insulin autoantibody (IAA) test at the same time, that one or both of these might have been positive in which case you might have type 1A (autoimmune) or even Late-onset Autoimmune Diabetes of Adulthood (LADA). You should ask your doctor about this.

The normal C-peptide and low current dose of insulin are against this though.

You might also have what is now called type 1B or idiopathic diabetes which occurs in only about 5% of Caucasian new onset cases. The exact pathology here is not yet understood except that these individuals are antibody negative. About half of the subjects can gradually do without insulin after an onset of insulin dependence indistinguishable from type 1A, although the evidence is that they are likely to need insulin again eventually.

Finally, you might have type 2 diabetes accounting for the normal C-peptide and what looks like a low dose of insulin for an adult.

There are indeed other possibilities, but the problem is that disentangling them can be a tiresome and expensive business, and in the end, the goal of management, irrespective of the exact molecular explanation, is to contain blood sugar levels as near as possible to normal without producing hypoglycemia.