Measurement of the Kidney Function in Patients with Rheumatoid Arthritis: Plasma Cystatin C versus ⁵¹Cr-EDTA Clearance

Abstract

Background/Aim: Knowledge of the usefulness of cystatin C measurement in the detection of chronic kidney disease in patients with rheumatoid arthritis (RA) is scant. The purpose of this study was to evaluate the ability of plasma cystatin C- and creatinine-based methods to predict glomerular filtration rate (GFR) and classify chronic kidney disease in RA patients. Methods: The study population consisted of 64 RA patients aged 41–86 years. Comparisons were made between measured plasma creatinine, cystatin C, creatinine clearance and GFR estimated by the Cockcroft-Gault (CG) and the Modification of Diet in Renal Disease (MDRD) formulas. The plasma clearance of ⁵¹Cr-EDTA served as a reference. Results: The Pearson correlation coefficients between plasma clearance of ⁵¹Cr-EDTA and the markers of GFR were calculated. The correlation coefficients were 0.800 for plasma creatinine, 0.863 for cystatin C, 0.866 and 0.904 for GFR values estimated by MDRD and CG and 0.922 for plasma creatinine clearance. Statistically significant differences were detected between the correlation coefficients of plasma creatinine and GFR estimated by CG (p = 0.0412) and plasma creatinine and creatinine clearance (p = 0.0099). Creatinine clearance and the MDRD and CG formulas proved to be better at identifying GFR <90 ml/min than plasma creatinine or cystatin C. Conclusion: We recommend using the CG formula or creatinine clearance for the estimation of the GFR of RA patients instead of solely creatinine or cystatin C in clinical work.

Cystatin C is a sensitive marker for detecting a reduced glomerular filtration rate when assessing chronic kidney disease in patients with rheumatoid arthritis and secondary amyloidosis

“…Although serum cysC appears to be a more convincing marker of renal function than serum Cr in patients with RA (2,13,14), some contradictory results have also been reported (15). This study provides additional evidence to support the advantage of serum cysC measurements in patients with RA.…”

Should We Continue to Use the Cockcroft-Gault Formula?

“…However, most drug-dosing recommendations are based on the Cockcroft-Gault (CG) [3] formula, which estimates the creatinine clearance (CrCl). Additionally, CG remains widely used in clinical practice and recent articles and reviews continue to support its use [4,5,6,45,47,63]. …”

The prognosis of severe lupus nephritis based on the Modification of Diet in Renal Disease (MDRD) Study estimated glomerular filtration rate

“…if the GFR decreases from 100 to 50 ml/min, the SCr in a small woman may increase from 0.5 to 1.0 mg/dl and, thus, still be within normal limits despite a 50% reduction in GFR). Karstila et al 10 found that the SCr was normal in 19% of rheumatoid arthritis patients with significant renal insufficiency (<60 ml/min/1.73 m 2 ) as determined by an EDTA clearance. This is consistent with our observation that 18% of patients with a normal SCr had a MDRD eGFR of <60 ml/min/ 1.73 m 2 .…”

“…11,12 Recent studies in patients with rheumatoid arthritis and systemic lupus erythematosus have found the MDRD equations for calculating eGFR to be superior to SCr or CrCl in measuring renal function. 9,10 As a result, it has been recommended that the MDRD-based determination of eGFR be used to assess and monitor renal function in patients with lupus nephritis. 13,14 To date no studies have assessed the prognosis of severe lupus nephritis based on the baseline level of eGFR.…”