Prognostic Value of Isolated High Serum Cystatin C Levels Without Glomerular Filtration Rate Reduction

Abstract OBJECTIVES: Cystatin C is increasingly used as a marker of renal function as a complement or alternative to serum creatinine and GFR calculated from it. However, cystatin C is also a marker of inflammation. We have assessed its efficacy as a predictor of mortality in a group of patients with increased cystatin C and GFR > 60 ml/min. DESIGN AND METHODS: We included 608 patients seen at our hospital, 65.9% of whom were male and 34.6% had diabetes mellitus. The mean age was 58.5±14.5 years and a mean GFR of 64.1±33.5 ml/min. Patients were divided into 3 groups: CONTROL (normal cystatin C and GFR > 60 ml/min, age 53.3±12.8 years, GFR 96.6±22.4 ml/min, n=193), INCREASED CYSTATIN (increased cystatin C and GFR >60 ml/min, age 58.9±13, 1 years, GFR 72.2± 10.4 ml/min, n = 40 ) and CKD (chronic kidney disease, increased cystatin C and GFR <60 ml/min, age 61.4±14.8 years, GFR 36.0±12.7 ml/min, n = 160). The relationship with overall mortality was analyzed using the survival curve by Kaplan-Meier method. RESULTS. Mean cystatin C was 0.75±0.13 mg/l, versus 1.79±0.54 in the CKD group and 1.14±0.14 mg/l, p<0.001 ANOVA). In the CONTROL group survival was 93.9% at five years, compared to 78.8% in the ERC group and 82.3% in the INCREASED CYSTATIN group (p < 0.001 Log Rank). Five-year survival before renal replacement therapy was also different for the ERC group (73%, p < 0.001 Log Rank) but not between the other two groups (CONTROL 99.0%, INCREASED CYSTATIN 94.3% p = 0.08 Log Rank). CONCLUSIONS. The presence of increased plasmatic levels of cystatin C in patients with GFR > 60 ml/min was a predictor of increased mortality but not of progression to end-stage renal failure. These results confirm the interest of routinely measuring cystatin C in our patients.