Table 3. Characteristics of the included studies.
| Study | Clinical setting | Population | Calendar year | Index test | Reference standard | Study design | N | Follow-up duration | RF/ACPA (%) | Symptoms duration | Joint count |
| Alves | Early arthritis | ≥1 swollen joint for less than 1 year; ≥16 years old, no history of trauma or exertion. MTX: 64/231 | 2004–2008 | ACR/EULAR 2010 classification criteria | MTX | Retrospective cohort | 231 | 12 months | 26/19 | 3.47 months | 44 |
| Berglin | Early arthritis | ≥1 swollen joint; no alternative diagnosis; ≤1 year symptom duration; ≥1 year of follow-up. MTX: 230/313 | n.a. | ACR/EULAR 2010 classification criteria | MTX | Retrospective cohort | 313 | 12 months | 60/64 | 4 months | n.a. |
| Britsemmer | Early arthritis | >18 years old; ≥2 swollenjoints; symptom duration of<2 years; no prior DMARDs.MTX: 354/455 | 2000–n.a. | ACR/EULAR 2010 classification criteria | MTX | Retrospective cohort | 455 | 12 months | 42.6/52 | 5.6 months | n.a. |
| Cader | Early arthritis | ≥1 swollen joint;; ≤3 months of symptom duration; ≥18 months follow-up. MTX: 74/205; DMARDs: 102/205 | n.a. | ACR/EULAR 2010 classification criteria | MTX DMARDs | Retrospective cohort | 205 | 18 months | 56/59 | 1.37 months | 66 |
| Kanenko | Early arthritis | joint symptoms (arthralgia, joint swelling and morning stiffness); no previous treatment; no diagnosis DMARDs: 54/82 | 2009–2010 | ACR/EULAR 2010 classification criteria | DMARDs | Retrospective cohort | 82 | 0–3 months | 66/61 | 4 months | n.a. |
| Kawashiri | Early arthritis | suspicion of RA; symptom duration <1 year; no alternative diagnosis; no previous DMARDs. DMARDs: 37/69 | 2010–2011 | ACR/EULAR 2010 classification criteria | DMARDs | Prospective cohort | 69 | 3 months | 49/36 | 4 months | n.a. |
| Nakagomi | Early arthritis | musculoskeletal symptoms <3 years; no alternative diagnosis. MTX:83/117 | n.a. | ACR/EULAR 2010 classification criteria | MTX | Prospective cohort | 117 | 12 months | n.a./n.a. | n.a. | 28 |
| Sakellariou | Early arthritis | patients with RA or UPA. MTX: 202/26; DMARDs: 211/266 | 2005–2010 | ACR/EULAR 2010 classification criteria | MTX DMARDs | Retrospective cohort | 266 | 12 months | 33/n.a. | 3.07 months | 44 |
| Tamai | Early arthritis | early arthritis; no alternative diagnosis. DMARDs: 97/138 | n.a. | ACR/EULAR 2010 classification criteria | DMARDs | Prospective cohort | 138 | 12 months | n.a. | 3 months | n.a. |
| Van der Linden | Early arthritis | arthritis confirmed by physical examination; <2 years symptom duration. MTX: 445/2258; DMARDs: 1066/2258 | 1993–2009 | ACR/EULAR 2010 classification criteria | MTX DMARDs | Retrospective cohort | 2258 | 12 months | 30/29 | 5.7 months | 66 |
N: number of patients included; n.a.: not available; RF: rheumatoid factor; ACPA: anti-ciclic citrullinated peptide antibodies; MTX: methotrexate; DMARDS: disease modifying antirheumatic drugs; RA: rheumatoid arthritis; UPA: undifferentiated polyarthritis.