Clinical usefulness of serum cystatin C as a marker of renal function

Abstract

Background: Accurate renal function measurements are important in the diagnosis and treatment of kidney diseases. In contrast to creatinine, the production of serum cystatin C has been extensively reported to be unaffected by body muscle mass, age, gender, and nutritional status.

Methods: Our study included 37 samples from diabetic chronic kidney disease (CKD) patients for whom serum creatinine tests had been requested and 40 samples from a healthy populations in Dong-A University Hospital between May 2010 and June 2010. The assay precision (i.e., the coefficient of variation) and the reference range of the serum cystatin C test were evaluated. We compared the estimated glomerular filtration rates (GFRs) based on cystatin C with those based on creatinine. Moreover, we investigated the influences of age, gender, weight, and muscle mass on serum creatinine and serum cystatin C.

Results: There was a positive correlation between GFR based on creatinine and that based on cystatin C (r=0.79, P<0.0001) among the diabetic CKD patients. Serum creatinine and cystatin C were significantly correlated with body weight and muscle mass, but the strengths of these correlations were greater for serum creatinine. The precision study revealed excellent results for both the high and low controls. The 95% reference interval of cystatin C in the healthy population was 0.371 to 1.236 mg/L.

Conclusion: Based on these results, we conclude that, despite the strong correlation between serum creatinine and cystatin C, cystatin C is less affected by weight and muscle mass and might represent a better alternative for the assessment of renal function.

Keywords: Renal function; Serum creatinine; Serum cystatin C.

Fig. 1

Strong correlations between the glomerular filtration rate (GFR) measurements based on the Modification of Diet in Renal Disease equation and those based on the new equation in the chronic kidney disease patients (A; r=0.79, P<0.0001) and the healthy individuals (B; r=0.36, P=0.01). It is commonly accepted that correlation coefficients (r values) between 0 and 0.2 indicate no correlations, those between 0.2 and 0.4 indicate weak low correlations, those between 0.4 and 0.6 indicate moderate correlations, and those above 0.8 indicate strong correlations.

Fig. 2

Associations of serum creatinine and cystatin C with body weight, muscle mass, and age in the healthy individuals. (A) The correlation between serum creatinine and body weight (r=0.64, P<0.0001). (B) The correlation between serum creatinine and muscle mass (r=0.71, P<0.0001). (C) The correlation between serum creatinine and age (r=0.23, P=0.1462). (D) The correlation between serum cystatin C and body weight (r=0.48, P=0.0019). (E) The correlation between serum cystatin C and muscle mass (r=0.48, P=0.0021). (F) The correlation between serum cystatin C and age (r=0.16, P=0.3089).

Fig. 3

Associations of serum creatinine and cystatin C with body weight, muscle mass and age in the diabetic chronic kidney disease patients. (A) The correlation serum creatinine and body weight (r=-0.05, P=0.7348). (B) The correlation between serum creatinine and height (r=-0.12, P=0.4708). (C) The correlation between serum creatinine and age (r=-0.003, P=0.9833). (D) The correlation between serum cystatin C and body weight (r=-0.29, P=0.0745). (E) The correlation between serum cystatin C and height (r=-0.24, P=0.1360). (F) The correlation between serum cystatin C and age (r=0.16, P=0.3384).