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November 2, 2000

Diagnosis and Symptoms

Question from Northborough, Massachusetts, USA:

Is there a difference between a GAD test and a GAD antibody test? We are trying to determine if our nine year old daughter, who was diagnosed with type 1 diabetes, actually has type 2 diabetes. The pediatric endocrinologist was reluctant to run an islet cell antibody and a GAD antibody test since she was diagnosed 11 months ago. Her results came back at 0.5 for the islet cell antibody with less than 0.5 being borderline and less than 2.5 on the GAD with greater than 2.5 being negative. The pediatric endocrinologist says they ran the wrong test and those 2.5 results don't mean anything. I called the lab, spoke with a supervisor and they said they ran the correct test. The GAD test is the GAD antibody test. No one seems to be able to help me nor does her pediatric endocrinologist feel they should rerun the test.

Answer:

The laboratory is right; the test was the GAD antibody test, but your endocrinologist is also right in saying that a negative test at this stage is not worth repeating and not very meaningful. Many centers now test for three antibodies at the optimal time which is at initial diagnosis, in part to distinguish type�1A or autoimmune diabetes, and, in part, to be able to predict how long the honeymoon period will last. With the islet cell antibody (ICA) test, it also makes a difference whether the old histological test was used, which is not always reliable, or whether the newer anti ICA-512 immunoassay was done.

Nearly all new onset cases in Caucasian families that require insulin acutely at diagnosis have type 1A or autoimmune diabetes and will require insulin in some form for the rest of their lives. It is also possible that, at 11 months after diagnosis, your daughter is still in the honeymoon period, and that is why you have been considering type�2. Children with the latter diagnosis are usually significantly overweight and have a family history of type 2 diabetes and the antibody test is unequivocally negative. It is possible that your daughter has type�1B diabetes which is common in African American and Hispanic families, but less than 5% in Caucasians. It is of some importance because about 50% can be manage after some weeks without insulin. Again, the antibody test is negative.

DOB