Background/Purpose: In rheumatoid arthritis (RA), women may be less likely to achieve clinical remission. These sex differences remain incompletely understood and might relate to differences in performance of disease activity measures, rather than biological sex differences. We evaluated sex differences in remission and low disease activity in patients with RA, comparing composite disease activity measures and definitions.

Methods: This longitudinal cohort study utilized data from the Veterans Affairs Rheumatoid Arthritis registry. Participants fulfilled ACR criteria for RA. Remission and low disease activity were defined based on composite scores (DAS 28 joints with ESR [DAS28-ESR], DAS 28 joints with CRP [DAS28-CRP], clinical disease activity index [CDAI], routine assessment of patient index data 3 [RAPID3]). We also studied achievement of low disease activity based on individual measures applying Boolean and other published criteria (tender joint count 28 joints [TJC28], swollen joint count 28 joints [SJC28], ESR, CRP, physician global assessment [PhGA], patient global assessment [PtGA]). We assessed 1) the likelihood of point remission at any time and 2) the time to sustained remission (2 consecutive visits) among those not in remission at enrollment. Logistic regression models incorporated generalized estimating equations to account for repeated disease activity measures and adjusted for age, race, smoking, and disease duration. Multivariable Cox proportional hazard models assessed differences in the time to sustained remission.

Results: At enrollment, women (n=252, 10.2%) were younger, less likely to be smokers, used less prednisone, and had fewer comorbidities. Considering all points in time, the odds of remission for women were lower only for DAS28-ESR [OR 0.71, (95% CI 0.55, 0.91), p<0.01] (Table 1). In contrast, women were more likely to attain CDAI low disease activity [OR 1.36, (95% CI 1.08, 1.73), p=0.01]. Women were more likely to achieve favorable individual measures- low SJC28, CRP, and PhGA, except for having an ESR <30 mm/hour [OR 0.72, (95% CI 0.57, 0.90), p<0.01]. Using an age-, sex-specific definition, women were more likely to achieve a low ESR [OR 1.32, (95% CI 1.05, 1.64), p=0.02]. In Cox models, women were less likely to reach sustained remission only by DAS28-ESR [HR 0.53, (95% CI 0.35 – 0.80), p<0.01]. There were no significant differences in sustained remission rates using DAS28-CRP, CDAI, or RAPID3.

Conclusion: The comparison of remission rates between men and women varied greatly based on the composite disease activity measure selected. Sex- specific differences in the ESR bias towards lower rates of remission among women using DAS28-ESR. This study suggests selection of disease activity measure may have influenced prior research suggesting low remission rates in women and illustrates the need for sex-specific treatment targets for the DAS28-ESR.