Hi CT mom,
Yes, you can have a positive RF for lupus; you can also have a positive ANA for rheumatoid arthritis. These blood tests are only markers. Actually, a positive rf is implicated in a lot of things besides RA, and many people have a positive ANA but are perfectly healthy. Go figure? It would be best if you see a rheumatologist, but a fair amount of clinical suspicion is also necessary for a dx. I only have a slightly positive rf, but because of my young age, and symmetrical joint swellings, etc..., I was dx with RA and I've been treated for about 4 years now.
You can learn a lot more about rf if you search this site. There were some earlier postings by Erin that had tons of great information on this antibody and what diseases it can be found in.