Table 1.

Characteristics of the study patients (N = 2,748). For time-varying characteristics (e.g., sacroiliac tenderness), current and prior presence are included.

Median age in years (IQR)	12.0 (7.7 – 15.4)
Female, n (%)	1,996 (73%)
Median disease duration in years (IQR)	3.9 (1.8 – 7.2)
ILAR JIA categories, n (%)
Systemic arthritis	246 (9%)
Persistent oligoarthritis	724 (26%)
Extended oligoarthritis	224 (8%)
RF− polyarthritis	802 (29%)
RF+ polyarthritis	200 (7%)
Enthesitis related arthritis	286 (10%)
Psoriatic arthritis	170 (6%)
Undifferentiated arthritis	62 (2%)
Missing or “Other”	34 (1%)
HLA-B27 positive, n (%)	210 (8%)
CCP antibody positive, n (%)	114 (4%)
Sacroiliac tenderness, n (%)	264 (10%)
Enthesitis, n (%)	324 (12%)
Uveitis, n (%)	304 (11%)
Inflammatory bowel disease, n (%)	53 (2%)
Psoriasis rash, n (%)	143 (5%)
Radiographic joint damage, n (%)	588 (21%)
ACR treatment groups, n (%)
History of arthritis of ≤ 4 joints	1,045 (38%)
History of arthritis of ≥ 5 joints	1,443 (53%)
Systemic Arthritis	246 (9%)

IQR = interquartile range; ILAR = International League of Associations for Rheumatology; JIA = juvenile idiopathic arthritis; RF = rheumatoid factor; CCP = cyclic citrullinated peptide; ACR = American College of Rheumatology