Assessment of renal function in renal transplant patients using cystatin C. A comparison to other renal function markers and estimates

To date, little evidence is available to define the role of cystatin C in p atients with renal transplants. Thus, to assess, whether cystatin C (CysC) provides better information on renal function than other markers, CysC, cre atinine clearance (CrCl), serum creatinine (SCr), beta (2)-microglobulin (b eta (2)-M), and I-125-Iothalamate clearance were determined in 30 patients. Correlation and ROC curves were obtained and characteristics like sensitiv ity and specificity were calculated. Further, to evaluate the usefulness of these markers for monitoring, intraindividual coefficients of variation fo r CysC and SCr measurements were compared in 85 renal transplant patients. CysC correlated best with GFR, whereas SCr, CrCl and beta (2)-M all had low er correlation coefficients. CysC was superior to SCr, even when renal func tion equations of were used. The diagnostic accuracy of CysC was significan tly better than SCr, but did not differ significantly from CrCl and beta (2 )-M. Together, our data show that in patients with renal transplants, CysC has a similar diagnostic value as CrCl. However, it is superior to determin ations of SCr. The intraindividual variation of CysC is significantly great er than that of SCr. This might be due to better ability of CysC to reflect temporary changes especially in mildly impaired GFR, most critical for ear ly detection of rejection and other function impairment. In conclusion, Cys C allows for easy and accurate assessment of renal function (GFR) in steady state renal transplant patients and is clearly superior to the commonly us ed serum creatinine.