Development of reduced kidney function in rheumatoid arthritis.

BACKGROUND: Rheumatoid arthritis (RA) is associated with a variety of kidney disorders. However, it is unclear whether the development of reduced kidney function is higher in patients with RA compared to the general population.

STUDY DESIGN: Retrospective review.

SETTING & PARTICIPANTS: Incident adult-onset RA cases (813) and a comparison cohort of non-RA individuals (813) in Olmsted County, MN, in 1980-2007.

PREDICTOR: Baseline demographic and clinical variables.

OUTCOMES: Reduced kidney function: (1) estimated glomerular filtration rate (eGFR)<60mL/min/1.73m(2) and (2) eGFR<45mL/min/1.73m(2) on 2 consecutive occasions at least 90 days apart; cardiovascular disease (CVD); and death.

MEASUREMENTS: The cumulative incidence of reduced kidney function was estimated adjusting for the competing risk of death.

RESULTS: Of 813 patients with RA and 813 non-RA individuals, mean age was 56±16 (SD) years, 68% were women, and 9% had reduced kidney function at baseline. The 20-year cumulative incidence of reduced kidney function was higher in patients with RA compared with non-RA participants for eGFR < 60mL/min/1.73m(2) (25% vs 20%; P=0.03), but not eGFR<45mL/min/1.73m(2) (9% vs 10%; P=0.8). The presence of CVD at baseline (HR, 1.77; 95% CI, 1.14-2.73; P=0.01) and elevated erythrocyte sedimentation rate in patients with RA (HR per 10-mm/h increase, 1.08; 95% CI, 1.00-1.16; P=0.04) was associated with increased risk of eGFR<60mL/min/1.73m(2). eGFR<60mL/min/1.73m(2) was not associated with increased risk of CVD development in patients with RA (HR, 0.99; 95% CI, 0.63-1.57; P=0.9), however, a greater reduction in GFR (eGFR<45mL/min/1.73m(2)) was associated with increased risk of CVD (HR, 1.93; CI, 1.04-3.58; P=0.04).

LIMITATIONS: Reduced kidney function was defined by estimating equations for kidney function. We are limited to deriving associations from our findings.

CONCLUSIONS: Patients with RA were more likely to develop reduced kidney function over time. CVD and associated factors appear to play a role. The presence of RA in individuals with reduced kidney function may lead to an increase in morbidity from CVD development, for which awareness may provide a means for optimizing care.