So I've had this issue too and was checked by one of the best rheumatologist who specializes in Sjogren's, or so they say. He couldn't find any signs, serum or otherwise. The only test he didn't run is the lip biopsy, which he said he wouldn't perform because there was no other sign. Of course, in addition to dry mouth, throat, and very wet eyes at time and itchy and dry at others, I had every other symptom of the illness. But no lip biopsy was done. I thought perhaps I should push for a lip biopsy, but no one will go over his head, since he's such a big shot and I'm not quite sure I have it anyway, since the disease is so much more common among women than men. Perhaps I'll pursue it again at some point, but at this point even my dry mouth and throat have mostly dissipated and I've come to see that my dry mouth is ore closely associated with a low-carb and ketogenic diet.