Background/Purpose: Many medications used in the treatment of rheumatoid arthritis (RA) impact renal function. Some of these may be contraindicated in the presence of a certain degree of renal failure or may require dosage adjustment. Product monograph of different molecules such as hydroxychloroquine (HCQ), methotrexate (MTX), sulfasalazine (SSZ), tofacitinib (TOFA) address the issue with different nomenclature. A glomerular filtration rate (GFR) cut-off point of 60 mL/min/1.73 m² is often mentioned for dose adjustment or contraindication. The objective of this work is to evaluate the proportion of patients with impaired renal function at the moment of initiation of RA treatment.

Methods: The data of all patients affected by RA starting a csDMARD, bDMARD or tsDMARDS were extracted from the Rhumadata® registry. For those patients, the estimated GFR (eGFR) was assessed using the CKD-EPI equation and the MDRD formula. eGFR are presented in five years age groups for both men and women.  Results are expressed as mean ± standard deviation, range, percentiles (5, 25, 50, 75 and 95) and the proportion of patients an impaired renal function (IRF) (i.e. an eGFR below 60 ml/min/1.73 m²). Potential predictors of IRF include age at diagnosis, gender, disease duration, exposure to csDMARDS or b or ts DMARDs, hypertension, CVD, Charlson comorbidity index. The use of “contraindicated” molecules is explored.

Results: Overall eGFR was obtained for 609 men and 1853 women. In men, mean eGFR in the 25-29, 55-59 and 75-79-years age groups are 125±10, 92±15 and 69±16 ml/min/1.73 m². In women, these estimates are 115±14, 87±16 and 70±17 ml/min/1.73 m². No patients below 45 years of age has an IRF. After this age, the proportion of men with an IRF increases from 5.1% in the 45-49-years age group to 21.2% in the 75-79-years age group. In women, these same proportions are 2.3 and 24.2%. The results of a stepwise forward selection logistic regression predicting IRF retained age at diagnosis (OR and 95% confidence interval=1.093 (1.073, 1.112)), gender ((women vs. men) 1.929 (1.278, 2.913)), disease duration (1.111 (1.087,1.136)) and hypertension (3.271 (2.116, 5.056)). The CKD-EPI equation and the MDRD formula identically classified 99% of patients as having (6%) or not having (93.0%) IRF. MTX, SSZ, HCQ and Tofacitinib are respectively prescribed for 78%, 10%, 62% and  6% of patients without IRF. These proportions are 63%, 9%, 52% and 4% among patients with IRF, the differences being statistically significant for MTX and HCQ.

Conclusion: As expected, eGFR decreases with age in both groups. Patients in all age groups after 45 years old may have an eGFR inferior to 60 ml/min/1.73 m². Below 55 years old, less than 5% of our population has less than 60 ml/min/1.73 m² of GFR as measure by CKD-EPI equation. Physicians prescribe less MTX, SSZ, HCQ and Tofacitinib to patients with IRF.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/profile-of-renal-function-in-patient-suffering-from-rheumatoid-arthritis/