The ring finger on my left hand appeared swollen and hurt when I work up this morning. I do not recall that I hit it with anything, twisting it, or got any insect bite. What could it be ?
It is possible, as my first noticeable symptom was a swollen toe joint that happened overnight. Howver, I was also experiencing fatigue and morning stiffness, which I wasn't so aware of until the toe joint became swollen and painful, so while this could signal RA, if you are not experiencing any other symptoms, it could very well be something much more innocent.
If you are experiencing fatigue and/or morning stiffness, or if the swelling doesn't go down or respond to anti-inflammatories (like aleve) or icing/heat treatments, then I would go to see your doctor to talk about what could be behind it. IF it is RA, it is important to get a diagnosis as early as possible so that you can begin treatment quickly and prevent as much damage to your joints as possible.
Hope this helps, and that it's just a swollen finger!