Table 1

Baseline demographic and clinical parameters

CharacteristicNo arthritis developed
N=40*
Arthritis developed
N=15
p Value
Sex, female (n (%))28 (70)9 (60)0.481
Age (years) (mean (SD))44 (12)47 (8)0.471
Smoking history, ever† (n (%))21 (53)14 (93)0.005
Pack years‡ (median (IQR))10 (4–20)15 (10–24)0.129
BMI ≥ 25, kg/m2 (n (%))18 (45)13 (87)0.006
IgM-RF positive (n (%))24 (57)9 (60)0.847
IgM-RF level low positive (n (%))§15 (62)4 (44)0.350¶
IgM-RF level high positive (n (%))§9 (38)5 (56)
ACPA positive (n (%))24 (60)12 (80)0.165
ACPA level§ (kAU/L) (median (IQR))465.5 (69.5–1229.8)452.0 (103.0–2518.8)0.585
IgM-RF and ACPA both pos. (n (%))8 (20)6 (40)0.129
  • p Values <0.05 in bold.

  • *Seven individuals have been at risk for arthritis development for a shorter period of time: two patients have started with hydroxychloroquine for arthralgias, and two with anti-TNF therapy because of a diagnosis of ankylosing spondylitis (n=1) or Crohn's disease (n=1). Three individuals were lost to follow up after some time.

  • †Smoking history: never smoked: 0 pack-years; ever smoked: >0 pack-years.

  • ‡Only in smokers.

  • §Only in positive individuals: low positive: ≤3 times upper limit of normal (ULN), high positive: >3 times ULN (according to the 2010 ACR/EULAR criteria for RA17 ,18).

  • ¶Using χ2 test for frequencies of low and high positivity of IgM-RF in the two outcome groups.

  • ACPA, anti-citrullinated protein antibodies; BMI, body mass index; IgM-RF, IgM-rheumatoid factor; RA, rheumatoid arthritis.