Dear Ugo,

I am actually working on cystatin C, and maybe I can give you some hints on the issue.

Obviously, the best global index of renal function is the glomerular filtration rate (GFR). Up to date, the reference standard for GFR measurement is inulin clearance, but the most commonly used marker in clinical practice is serum creatinine, alone or together with 24-hour urine collections for creatinine clearance, albeit the accuracy of these markers is limited by many factors (reliability of urine collection, muscle mass, diet, age, etc.).

Cystatin C meets all criteria for being a marker of GFR (stable production rate and circulating levels not affected by other pathological changes, freely filtered at the glomerulus without tubular reabsorption or secretion) [1-2]. GFR is generally estimated through cystatin C using the formula GFR = 74.835/(serum cystatin C)1.333 [3].

In a meta-analysis, it has been demonstrated that cystatin C is superior to serum creatinine as a marker of kidney function in general population [4]. Also, cystatin C has proven itself as a better estimator of GFR even in contrast-induced nephropathy patients [5].

Hoping to have been of help,

Best Regards,

1. Filler G, et al. Cystatin C as a marker of GFR – history, indications, and future research. Clin Biochem 2005;38:1-8.

2. Fliser D, et al. Serum cystatin C concentrations as a marker of renal dysfunction in the elderly. Am J Kidney Dis 2001;37:79-83.

3. Levey As, Coresh J, Balk E, et al. National Kidney Foundation practice guidelines for chronic kidney disease: evaluation, classification, and stratification. Ann Intern Med 2003;139:137-147.

4. Dharnidharka RV, Kwon C, Stevens G. Serum cystatin C is superior to serum creatinine as a marker of kidney function: A meta-analysis. Am J Kidney Dis 2002;40(2):221-226.

5. Kimmel M, et al. Improved estimation of glomerular filtration rate by serum cystatin C in preventing contrast induced nephropathy by N-acetylcysteine or zinc-preliminary results. Nephrol Dial Transplant. 2008;23(4):1241-5.