The stages of rheumatoid arthritis -- sometimes called RA -- are defined by the 2008 recommendations of the American College of Rheumatology as the following:
Early disease: Symptoms of active rheumatoid arthritis for fewer than 6 months
Intermediate disease: Symptoms of active rheumatoid arthritis for 6 to 24 months
Longer disease: Symptoms of active rheumatoid arthritis for more than 24 months
Note that these stages are meant to be applied to rheumatoid arthritis patients who haven't been treated with disease-modifying antirheumatic agents (DMARDs).
Rheumatoid arthritis is also usually given an "activity" rating of mild, moderate, or severe, corresponding to a patient's current level of inflammation.
To assess rheumatoid arthritis activity, the doctor will consider the following factors:
The patient's report of symptoms and their impact on day-to-day function
The doctor's assessment of how many joints are involved, how badly the joints are affected, and whether any non-joint symptoms are present
The level of inflammation as measured by blood work
Inflammation and joint damage as measured by X-rays
Doctors use the current stage and activity of a patient's rheumatoid arthritis to determine what type of medication to prescribe.
There are also some patients who've had rheumatoid arthritis for a long time and have had their joints badly damaged over the years. These patients, who may now have low levels of inflammation, are sometimes referred to as being in "end-stage" rheumatoid arthritis. (Note that end-stage rheumatoid arthritis is not a terminal disease; it's just an advanced stage that not everyone develops.)