Disease activity of rheumatoid arthritis and kidney function decline: a large prospective registry study.

Introduction: Chronic kidney disease (CKD) is a common comorbidity of rheumatoid arthritis (RA). The association of longitudinal RA disease activity with long-term kidney function has remained uncertain.

Method: We analysed a multicentre prospective RA registry in the USA from 2001 to 2022. The exposure was updated time-averaged Clinical Disease Activity Index (TA-CDAI) categories from study enrolment. The primary outcome was a longitudinal estimated glomerular filtration rate (eGFR) change. Secondary outcomes included developments of CKD stage G3a (eGFR<60 mL/min/1.73 m) and stage G3b (eGFR<45 mL/min/1.73 m). Results were adjusted for relevant time-fixed and time-varying covariates.

Results: 31 129 patients (median age: 58.0 years, female: 76.3%, median eGFR: 90.7 mL/min/1.73 m) contributed 234 973 visits and 146 778 person-years of follow-up. Multivariable mixed-effect linear model showed an average annual eGFR decline during follow-up in the TA-CDAI-remission group of -0.83 mL/min/1.73 m and estimated additional annual declines (95% CI) of -0.09 (-0.15 to -0.03) in low, -0.17 (-0.23 to -0.10) in moderate and -0.18 (-0.27 to -0.08) mL/min/1.73 m in high disease activity patients. Compared with TA-CDAI remission, adjusted HRs (95% CI) for CKD stage G3a during follow-up were 1.15 (1.01 to 1.30) in low, 1.22 (1.06 to 1.40) in moderate and 1.27 (1.05 to 1.52) in high disease activity; for CKD stage G3b, 1.22 (0.84 to 1.76) in low, 1.66 (1.12 to 2.45) in moderate and 1.93 (1.16 to 3.20) in high disease activity.

Conclusions: Higher RA disease activity was associated with accelerated eGFR decline and increased risk of clinically relevant kidney dysfunction. Future intervention studies should attempt to replicate the association between RA disease activity and eGFR.