Glomerular Filtration Rate Estimation using Cystatin C Levels Identifies Subclinical Renal Dysfunction in Patients with Rheumatoid Arthritis

BackgroundMethotrexate is widely used to treat rheumatoid arthritis (RA) but can cause very serious side effects, including pancytopenia, in patients with renal impairment who have an estimated glomerular filtration rate (GFR) of <60 ml/min/1.73m 2 . In patients with low muscle volume such as elderly patients, GFR can be measured as higher value when calculated using serum creatinine [eGFR(cre)], so more accurate estimation using cystatin C [eGFR(cys)] is preferred.MethodWe evaluated 173 patients with RA who visited Toranomon Hospital in 2019 for factors that may contribute to the difference between eGFR(cre) and eGFR(cys) [eGFR(cre−cys)]. Activities of daily living (ADL) (walking, 1 point; using a cane, 2 points; using a wheelchair, 3 points) was added as a parameter.ResultsIn univariate analysis using Spearman's rank correlation coefficient, eGFR(cre−cys) was negatively correlated with body weight, height, body surface area (BSA), subcutaneous fat area (SFA)/BSA, albumin, and creatinine kinase, and positively correlated with age, erythrocyte sedimentation rate (ESR), and urinary protein. eGFR(cre−cys) was higher in patients who used a cane or wheelchair than those who could walk unaided. Multiple regression analysis showed that ADL and age contribute significantly to eGFR(cre−cys). ConclusionPatients using a cane or wheelchair are susceptible to the higher eGFR(cre−cys) values and overestimation of eGFR(cre), resulting in failed detect subclinical renal dysfunction. For such patients, eGFR(cys) should be evaluated to prevent serious side effects of methotrexate that are easily developed on patients with renal dysfunction.