How do you interpret the presence of GAD antibody in a middle-aged patient with diabetes when all other type 1 diabetes antibodies are absent?

I tend to order these antibodies in those adults who do not have a very clear clinical picture to diagnose them as either 1 or 2, like a middle aged normal built male/female with no other comorbid conditions and negative family history too. Then, if GAD is negative, chance of have T1 is very very low, and I use oral agents and non-insulin therapy. If GAD is positive, I order IA-2 antibody, and decide therapy based on its result. The presence of GAD alone is challenging in lean built mildly diabe...

It depends on patient's clinical course of diabetes, controlled on orals vs insulin, BMI, family history DM. For a brittle DM patient, high GAD titer could indicate DM1 or LADA. For stable DM patients, the recommendation is to have 2 positive antibodies to diagnose DM1.