The answer must be yes, people without diabetes can have GAD antibodies and people with LADA may be diagnosed very early in the process. Others may be diagnosed when they are losing weight and are in effect just like a type 1 diagnosis (and some may be diagnosed as T2 but fail to respond to oral medications because of their rapidly failing beta cells)
Reference ranges seem to vary in the papers as do the units and so do the definitions of what constitutes LADA.
You will have to ask your doctor about the ref range used in your test .This from Southend path lab may help.
http://www.southend.nhs.uk/pathology-handbook/test-directory/test-directory-g-index/gad-antibodies/
Note that small numbers of GAD antibodies can be in relatives of people with T1.
There are several papers that suggest higher levels of GAD are associated with a quicker need for insulin and some that suggest that LADA itself may have two distinct types one more like T1, one with more insulin resistance and more like T2 or it could be a continuum with one end being more like type 1 and the other more like T2
http://www.diapedia.org/type-1-diabetes-mellitus/lada-latent-autoimmune-diabetes-of-the-adult
The papers all use different 'cut offs' , this is just a small sample of papers.
In the UKPDS study In the UK Prospective Diabetes Study 71 the risk of requiring insulin in patients with GADA levels of 20–37.4 units was 20%, but GADA levels of 37.5–101 units give a 50–75% risk.
But another study uses GADA titers > 20 U/ml as a cut off point between high and low titres
http://www.ncbi.nlm.nih.gov/pubmed/17435855
And yet another cut off of (>32 GADA U) for a high titre It also said that these people showed more evidence of autoimmunity with greater levels of other autoimmune antibodies (eg TPO, thyroid antibodies )
http://www.endocrine-abstracts.org/ea/0029/ea0029p562.htm
. One paper written by a British researcher says
It is important to note that there is large variation between laboratories with respect to GADA levels defining an abnormality, and caution should be exercised in using defined units; for our study, a cutoff of 70 World Health Organization units was used. Therefore, to accurately identify patients with LADA, perhaps a minimum level of GAD units should be selected within a definition
http://care.diabetesjournals.org/content/31/3/439.full
