Hi Jue
The tests that are done by the GPs, such as Rheumatoid Factor, are not done for RA diagnostic purposes and indeed a diagnosis cannot be made on these alone even if the RF test is positive. The only reliable test is the anti-CCP test done by a rheumatologist. This
link will explain the test in some detail and this
link from the NRAS site will also help answer questions about lab tests.
I had two friends diagnosed with Inflammatory Arthritis within two years of myself. In each case their's burned itself out within the first few years, mine didn't! There are many different types of Inflammatory Disease and each can be quite unique. My inflammatory markers were negative at the outset, but the anti-CCP wasn't available way back then. I had the anti-CCP checked recently with a view to changing medication and lo and behold I'm actually 'positive'! Probably have been since the start if the truth be known!
Your friend needs to be referred to rheumatology quickly if she suspects she may have RA. Have a look at
this from the RA awareness campaign.
Hope your friend is able to get some help.
Lyn x