Background: Because of the limitations of creatinine (Cr) as a marker for the glomerular filtration rate (GFR), cystatin C (CysC) has been proposed as an alternative substance. The aim here was to clarify the characteristics of CysC compared with Cr.
Methods: CysC and Cr were measured in 199 patients with chronic kidney disease. Regression analysis between CysC and Cr and comparisons of the effect of gender, inflammation, prescription of prednisolone, smoking and diabetes mellitus (DM) on these markers were performed. Sensitivity and specificity of CysC and Cr to discriminate estimated GFR of less than 50 ml/min/1.73 m(2) were computed and evaluated by the receiver-operating characteristic curve (ROC).
Results: The correlation coefficient between natural logarithmic Cr [ln(Cr)] and ln(CysC) was higher than that between these variables per se (0.941 vs. 0.906). When Cr was lower than 1.10 mg/dl, CysC rose more sharply than Cr. CysC divided by Cr (CysC/Cr) was higher in females (1.35 +/- 0.33 vs. 1.16 +/- 0.30; p < 0.001), in patients with elevated CRP (1.33 +/- 0.40 vs. 1.21 +/- 0.29; p < 0.001) and in patients prescribed with prednisolone (1.42 +/- 0.33 vs. 1.20 +/- 0.30; p < 0.001). A stepwise multiple linear regression model indicated that ln(CysC) was positively correlated with ln(Cr), age, female gender, prednisolone prescription, elevated CRP and DM (R = 0.964, p < 0.001). The area under the ROC curve of Cr was 0.900 and that of CysC was 0.925.
Conclusion: CysC is a promising marker for GFR because it was not gender- or age-related. However, inflammation, prednisolone and DM caused CysC to deviate higher than expected from GFR. CysC can rise sensitively in early renal dysfunction.