Background
Creatinine is the most widely used renal failure biomarker; however, it has a lot of drawbacks. One of the major drawbacks is the blind range (does not increase until 50% of the kidney deteriorates). On the other hand, cystatin C has gained more attention as a promising biomarker due to several advantages over creatinine. Cystatin C levels are elevated as soon as any mild defect in the kidney occurs. Furthermore, cystatin C is influenced by several non-renal diseases which provide an additional prognostic value for this promising biomarker.

Objectives
1. Study the effects of age, gender and smoking on cystatin C levels to. 2. Challenge the adoption of glomerular filtration rate equations for healthy population. 3. Compare the values generated from different glomerular filtration rate equations. 4. Evaluate the prognostic value of cystatin C for selected non-renal diseases.

Methods
Using cross sectional analyses, we established the relationship between cystatin C levels and non-renal predictors. The quantification of cystatin C was performed by high performance liquid chromatographic method, while for creatinine by a colorimetric enzymatic method.

Results
In the healthy volunteers the levels of cystatin C were slightly higher in men than in women and in individuals older than 50 years old than those under 50 years old and in smokers than non-smokers, however, statistical data confirmed a non-significant relationship with respect to the aforementioned factors. For the recruited patients suffering from (diabetes, hyper- and hypothyroidism and cardiac dysfunctions) a clear increase in cystatin C levels were observed with the exception of hypothyroidism patients in which a decrease in their cystatin C levels were observed.

Conclusion
Diabetes, thyroid and cardiac dysfunctions have a clear impact on the levels of cystatin C in human blood, whereas age, gender and smoking habit have no effect. Therefore, cystatin C could be considered as a useful biomarker of the aforementioned diseases, in turn, this requires extra precautions including the evaluation of several clinical conditions by physicians should CC is considered as a renal failure biomarker.