Table 2. American College of Rheumatology/European League Against Rheumatism 2010 classification criteria for rheumatoid arthritis.

Target population (Who should be tested?): Patients
1) who have at least one joint with definite clinical synovitis (swelling)*
2) with the synovitis not better explained by another disease†
Classification criteria for RA (score-based algorithm: add score of categories A-D; a score of 6/10 is needed for classification of a patient as having definite RA)‡
A. Joint involvement§
1 large joint¶	0
2-10 large joints	1
1-3 small joints (with or without involvement of large joints)#	2
4-10 small joints (with or without involvement of large joints)	3
>10 joints (at least 1 small joint)**	5
B. Serology (at least one test result is needed for classification)††
Negative RF and negative ACPA	0
Low-positive RF or low-positive ACPA	2
High-positive RF or high-positive ACPA	3
C. Acute-phase reactants (at least one test result is needed for classification)‡‡
Normal CRP and normal ESR	0
Abnormal CRP or abnormal ESR	1
D. Duration of symptoms§§
<6 weeks	0
>6 weeks	1
RA: Rheumatoid arthritis; RF: Rheumatoid factor; ACPA: Anticitrullinated protein antibody; CRP: C-reactive protein; ESR: Erythrocyte sedimentation rate. * Criteria are aimed at classification of newly presenting patients. In addition, patients with erosive disease typical of RA with a history compatible with prior fulfillment of 2010 criteria should be classified as having RA. Patients with longstanding disease, including those whose disease is inactive (with or without treatment) who, based on retrospectively available data, have previously fulfilled 2010 criteria should be classified as having RA. † Differential diagnoses vary among patients with different presentations, but may include conditions such as systemic lupus erythematosus, psoriatic arthritis, and gout. If it is unclear about relevant differential diagnoses to consider, an expert rheumatologist should be consulted. ‡ Although patients with a score of 6/10 are not classifiable as having RA, their status can be reassessed and criteria might be fulfilled cumulatively over time. § Joint involvement refers to any swollen or tender joint on examination, which may be confirmed by imaging evidence of synovitis. Distal interphalangeal joints, first carpometacarpal joints, and first metatarsophalangeal joints are excluded from assessment. Categories of joint distribution are classified according to location and number of involved joints, with placement into highest category possible based on pattern of joint involvement. ¶ Term “large joints” refers to shoulders, elbows, hips, knees, and ankles. # Term “small joints” refers to metacarpophalangeal joints, proximal interphalangeal joints, second through fifth metatarsophalangeal joints, thumb interphalangeal joints, and wrists. ** In this category, at least one of involved joints must be a small joint; other joints can include any combination of large and additional small joints, as well as other joints not specifically listed elsewhere (e.g., temporomandibular, acromioclavicular, sternoclavicular, etc.). †† Negative refers to international unit (IU) values that are less than or equal to upper limit of normal (ULN) for laboratory and assay; low-positive refers to IU values that are higher than ULN but three times ULN for laboratory and assay; high-positive refers to IU values that are three times ULN for laboratory and assay. Where RF information is only available as positive or negative, a positive result should be scored as low positive for RF. ‡‡ Normal/abnormal is determined by local laboratory standards. §§ Duration of symptoms refers to patient self-report of duration of signs or symptoms of synovitis (e.g., pain,swelling, tenderness) of joints that are clinically involved at time of assessment, regardless of treatment status.