| There is no official classification of 1.5. My doctor used it to define slow developping, type 1 diabetes (probably autoimmune) with little or no insulin resistance. This is otherwise known as LADA. Others define it differently and include MODY which is a genetic type of diabetes. The more I read the more I'm convinced that there are many different types of diabetes, all with slightly differing nuances.
As far as I can see from people on here.Some were initially diagnosed with type 2 but didn't fit the 'normal' pattern, conventional oral drug treatments didn't seem to work or they stopped working relatively quickly. Many but not all seem to have experienced weight loss.
For myself I was initially diagnosed as type 1.5 in hospital when I was admitted with high blood sugars and high ketones. I think that what caused the 1.5 diagnosis was:
a) I'd had symptoms for some time ( I privately had thought I had type 2 and thought all that a doctor would prescribe was a healthy diet and exercise which I already did) therefore not classic type 1, it was a slow onset... over at least 3 years.
b) Was by then very thin.
c) my age,52
d) once BS was lowered I needed 'normal' quantities of insulin to control it. I didn't apear to have much insulin resistance.
It was only then that they did the other lab tests as confirmation. They'd already told me I had 1.5. I understood that the tests (particularly anti GAD which is not positive in all cases) are not definitive in themselves
For a fairly recent summary of the various of LADA see Bandurska-Stankiewicz, LADA (just google it, my link didn't work )  | 
