My diagnosis is seronegative rheumatoid arthritis. That means my blood tests for things like rheumatoid factor and anti-CCP have come back negative. However my ESR test was 33 and my CRP (C-Reactive Protein) test came back at 102 (normal is around 8), which indicates some pretty major inflammation. Plus, I've been walking around with a low-grade fever since the beginning of December.
Those, combined with my history and physical exam, result in the diagnosis. Keep in mind that there is no one test that says, yes, you have rheumatoid arthritis.
I was lucky to get diagnosed so quickly because my symptoms came on so explosively (pretty much all my joints together, over the course of a 12-day period). Others aren't so fortunate and play a guessing game with their doctors for much longer.