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

Abstract

Objective: Chronic kidney disease is a predictor of end-stage renal disease, and evaluating the glomerular filtration rate (GFR) is necessary to make a definite diagnosis. We assessed the utility of serum cystatin C (cysC) for identifying a reduced GFR in patients who have rheumatoid arthritis (RA) with secondary amyloidosis.

Methods: Fifty patients with RA and secondary amyloidosis (mean age 60.9±11.2 years; 45 women) were evaluated. The revised 24-h creatinine clearance (r24-hC_Cr), which was determined by multiplying the original value by 0.719, was used as a reference for the GFR. The screening potential of the serum cysC and some estimates of the GFR calculated from the serum cysC (cysC-eGFR: eGFR_Hoek and eGFR_Rule) for detecting a reduced GFR (r24-hC_Cr<60 mL/min/1.73 m²) were analysed.

Results: Both cysC-eGFRs were strongly correlated with the r24-hC_Cr (eGFR_Hoek, r=0.846, p<0.001; eGFR_Rule, r=0.820, p<0.001). The difference between the average eGFR_Rule (37.1±31.2 mL/min/1.73m²) and average r24-hC_Cr (35.3±30.9 mL/min/1.73 m²) was small, whereas eGFR_Hoek and sCr-eGFR were higher than eGFR_Rule and r24-hC_Cr. In receiver operating characteristic (ROC) curve analyses of a reduced GFR, serum cysC gave a greater area under the curve (AUC=0.958) than the sCr-eGFR (0.939–0.942). The specificity and positive predictive value (PPV) reached 100% when serum cysC >1.365 mg/L was used.

Conclusions: Serum cysC can identify a reduced GFR more accurately than sCr-eGFRs. Serum cysC >1.09 mg/L (i.e. eGFR_Rule<60 mL/min/1.73 m²) could be a marker of a reduced GFR, and serum cysC >1.365 mg/L would strongly suggest a reduced GFR in patients who have RA with secondary amyloidosis.