AB0127 VERY STRONGLY POSITIVE RHEUMATOID FACTOR LEVELS (10-FOLD HIGHER THAN THE UPPER NORMAL RANGE) RATHER THAN “RHEUMATOID FACTOR POSITIVITY” PER SEARE ASSOCIATED WITH SMOKING IN FEMALE RA PATIENTS WITHOUT A HISTORY OF OCCUPATIONAL DUST AND FUME EXPOSURE
Authors: Daisy Kirtley, David Hutchinson
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> Rheumatoid factor (RF) forms part of the 2010 EULAR/ACR classification criteria<sup>1</sup>. A weakly positive RF is defined as up to 3-fold higher and a strongly positive RF &gt;3-fold higher than the upper normal range. However, a longitudinal study of individuals with RF levels at least 4-fold higher than the upper range of normal had an adjusted hazard ratio for RA development of 26 (95% CI 15 to 46) compared to only 6.0 (3.4 to 10) for individuals with levels 2 to 4-fold above the upper normal range<sup>2</sup>. We have recently reported median RFs of greater than 10-fold higher than the upper normal range in nodular RA which is far more prevalent in smokers than non-nodular RA<sup>3</sup>. We have arbitrarily defined this level of RF as very strongly positive as it defines a disease subtype. Additionally, RF levels are strongly associated with additive exposures to both smoking and industrial vapours, gases, dust and fumes (VGDF) in male RA, with only 8% having been exposed to neither VGDF nor cigarette smoke<sup>4</sup>. <h3>Objectives</h3> Accordingly, we have studied female RA in whom VGDF exposures are less common to compare RF levels in an appreciable number of smokers and non-smokers without the significant confounding effect of VGDF exposures to determine if smoking is specifically associated with a very strongly positive RF. <h3>Methods</h3> Medical record analysis yielded 241 female RA patients seen in clinic between January and June 2018 without exposures to industrial VGDF. These patients were stratified for a history of smoking. RF was measured with Tina-quant Rheumatoid Factors II Test System, by Roche Diagnostics Corporation at the time of RA diagnosis. A value of &lt; 14 IU/ml was considered as negative as per manufacturer guidelines, a RF weakly positive (14-42 IU/ml), RF strongly positive (42.1-140 IU/ml) and RF very strongly positive (&gt;140 IU/ml). <h3>Results</h3> There were 109 never smokers and 132 smokers with a median RF of 21 IU/ml and 53 IU/ml respectively, p&lt;0.05. In never-smokers significantly more were seronegative 46/109 (42%) vs. 32/132 smokers (24%),odds ratio (OR)=2.22 (95% confidence interval (CI)1.28-3.83, P=0.004). Of never smokers 22/109 (20%) were weakly RF positive and very similar to smokers 28/132 (21%).29/109 (27%) of never smokers were strongly RF positive and a similar proportion of smokers 37/132 (28%) were strongly RF positive. Finally in never smokers, only 12/109 (11%) very strongly RF positive compared to 35/132 (27%) of smokers, OR=2.89 (95% CI 1.41-5.89, p=0.004). <h3>Conclusion</h3> Considering female RA smokers and non-smokers, the difference in RF positivity was exclusively accounted for by an increased prevalence of a very strongly positive RF in female smokers. This suggests that smoking has an impact on very strongly positive RF levels rather than RF positivity per se without the important confounding factor of VGDF exposure. <h3>References</h3> [1] Aletaha D, et al. 2010 Rheumatoid arthritis classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Arthritis &amp; Rheumatism. 2010;62(9):2569-81. [2] Nielsen SF, et al. Elevated rheumatoid factor and long term risk of rheumatoid arthritis: a prospective cohort study. BMJ. 2012;345:e5244. [3] Murphy D, et al. Nodular rheumatoid arthritis (RA): A distinct disease subtype, initiated by cadmium inhalation inducing pulmonary nodule formation and subsequent RA–associated autoantibody generation. Medical hypotheses. 2019;122:48-55. [4] Murphy D, et al. Vapour, gas, dust and fume occupational exposures in male patients with rheumatoid arthritis resident in Cornwall (UK) and their association with rheumatoid factor and anti-cyclic protein antibodies: a retrospective clinical study. BMJ open. 2018;8(5):e021754. <h3>Disclosure of Interests</h3> None declared