Three years ago, I was diagnosed with type 2 diabetes. The symptoms of thrist, fatigue and frequent urination came on suddenly. I also lost about 12 pounds. I am overweight. I recently had antibody testing. I had just enough positive GAD antibodies to put me in the type 1/LADA classification. What is number on the GAD antibody test that separates type 1 from type 2? About what percentage of type 2 patients turn out to have type 1.5 diabetes?

The results of antibody tests are not really supposed to be reported as actual numbers any more; but rather as +ve or -ve. A positive test is meant to indicate that the level of antibody is more than three standard deviations above the normal. Not every laboratory that does the antibody testing, however, has gone to the expense of establishing a substantial number of normal values, so they express the test result as a figure without indicating how abnormal it is. In the case of your test, you should contact the laboratory director for an explanation of this point, remembering also that small differences in technique between laboratories may result in individually different normal ranges. As I expect you will learn, though levels of anti GAD antibodies in subjects with LADA tend to be intermediate between those for autoimmune diabetes and those for normal.

It really isn’t possible to give a figure for the proportion of type 2 diabetics who ultimately turn out to have LADA (Late Autoimmune Diabetes in Adults) or type 1.5 diabetes, as it used to be called, because it depends so much on the age of the subject and the enthusiasm of the doctor for antibody testing. Moreover, the distinction may not always be of great clinical import even though it may affect decisions on the use of insulin and on genetic counseling.

DOB