IMMCO is the company name of a provider of lab testing supplies and facilities, and they have two new tests for the diagnosis of Sjogrens: Salivary Protein 1 (SP- 1) Antibodies, IgG Western Blot, and Parotid Specific Protein (PSP) Antibodies, IgG Western Blot .
These tests are supposed to be more accurate and specific, and show antibody developement early in the disease process. I don't think they have been readily accepted as screening tests, but may be available as more advanced testing if you have tested negative to anti-SS-A and SS-B.
The ANA is a very non-specific test, often elevated in many autoimmune, infectious and other disease processes, and occasionally transiently elevated in healthy people.
Because they are new, they may not be readily available, may not be covered by insurance, and may be quite expensive. You may have to actually print information from the IMCO site and take it to your doctor, as he may not be aware of these tests yet.