The American Rheumatism Association 1987 revised criteria for the classification of rheumatoid arthritis:
1) morning stiffness in and around joints lasting at least 1 hour before maximal improvement
2) soft tissue swelling (arthritis) of 3 or more joint areas observed by a physician
3) swelling (arthritis) of the proximal interphalangeal, metacarpophalangeal, or wrist joints
4) symmetric swelling (arthritis)
Criteria 1 through 4 must have been present for at least 6 weeks.
5) rheumatoid nodules
6) the presence of rheumatoid factor
7) radiographic erosions and/or periarticular osteopenia in hand and/or wrist joints
Rheumatoid arthritis is defined by the presence of 4 or more criteria.
http://arthritis-research.com/pubmed/3358796
Arnett FC, Edworthy SM, Bloch DA, McShane DJ, Fries JF, Cooper NS, Healey LA, Kaplan SR, Liang MH, Luthra HS, et al. _Arthritis Rheum._ 1988 Mar;31(3):315-24.
