Factors contributing to discrepant estimated glomerular filtration values measured by creatinine and cystatin C in patients with rheumatoid arthritis

Abstract

This study aimed to clarify the factors underlying the discrepancy that has been noted between estimated glomerular filtration ratio (eGFR) measured using serum creatinine (Cr) and eGFR using serum cystatin C (CysC) in patients with rheumatoid arthritis (RA) and to identify those patients whose renal function should be evaluated using CysC. We retrospectively evaluated clinical features, disease activity, Steinbrocker radiological staging, and co-morbidities (diabetes mellitus, hypertension, dyslipidemia) in 238 RA patients. eGFR using serum creatinine (eGFR-Cr) and eGFR using serum cystatin C (eGFR-CysC) were calculated using the new Japanese coefficient-modified Modification of Diet in Renal Disease study equation. To clarify the cause(s) of differences of 20% or more between the two eGFRs, we divided our RA patients into Group A (eGFR-Cr/eGFR-CysC ≥ 1.2) and Group B (eGFR-Cr/eGFR-CysC < 1.2), and searched for factors independently related to Group A. Forty-five patients (18.9%) were assigned to Group A, and 193 (81.1%) to Group B. BMI (Odds Ratio [OR] 0.820, 95% confidence interval [CI] 0.675-0.996), Hb (OR 0.633, 95% CI 0.433-0.926), CK (OR 0.773 per 10 units, 95% CI 0.644-0.933), NSAID use (OR 0.099, 95% CI 0.020-0.494), diabetes mellitus (OR 6.024, 95% CI 1.508-24.390) and stage 4 Steinbrocker radiological stage (OR 10.309, 95% CI 2.994-35.714) were identified as independent relevant factors for Group A by a multifactorial analysis. Renal function in RA patients with low BMI, diabetes, anemia and low CK may be overestimated using eGFR-Cr alone, and such patients need to be evaluated using eGFR-CysC.

Figure 1

Relationship between eGFR-Cr and eGFR-CysC. eGFR-Cr; estimated glomerular filtration rate using creatinine. eGFR-CysC; estimated glomerular filtration rate using cystatin C. The correlation between eGFR-Cr and eGFR-CysC was significant (r = 0.715, p < 0.0001). However, 25 (13.8%) of 181 patients with eGFR-Cr ≥ 60 mL/min/1.73 m² showed eGFR-Cys < 60 mL/min/1.73 m².

Figure 2

Distribution of eGFR-Cr/eGFR-CysC using the histogram with a logarithmic scale on the X axis. eGFR-Cr; estimated glomerular filtration rate using creatinine. eGFR-CysC; estimated glomerular filtration rate using cystatin C. There was an inflection point at 1.2. Thus, we divided the patients into two groups by this point (greater than 20% discrepancy).