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?  

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.

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 lo...