NDT Advance Access published online on January 18, 2006
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfk083
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1 Department of Hospital Pharmacy, Erasmus MC, Dr Molewaterplein 40, 3015 GD Rotterdam, The Netherlands
* To whom correspondence should be addressed. Background. Several markers are available to estimate the glomerular filtration rate (GFR) in patients. Cystatin C is a relatively new marker and has been suggested as an alternative for creatinine. Numerous studies have been performed to evaluate the usefulness of cystatin C to estimate GFR. The aim of this study is to compare the renal extraction of cystatin C with that of 125I-iothalamate in hypertensive patients. Methods. Forty hypertensive patients with unilateral renal artery stenosis, and who used at least two antihypertensive agents, were studied. For the determination of the renal extraction ratio, blood samples were drawn simultaneously from the renal vein and the abdominal aorta. The renal extraction ratio was calculated as ([A]-[V])/[A], in which A is the plasma concentration of the compound from the abdominal aorta, and V is the plasma concentration of the compound from the renal vein. Results. The mean difference between the renal extraction ratio of cystatin C and that of 125I-iothalamate was 0.002. The 95% confidence interval (CI) for the mean difference was -0.036 to 0.032, which was not statistically significant. However, the limits of agreement were large (-0.271 and 0.267). Conclusions. Despite a lower reported glomerular sieving coefficient of cystatin C, the mean renal extraction of cystatin C was equal to the mean renal extraction of 125I-iothalamate in hypertensive patients, suggesting tubular secretion of cystatin C. Combined with the large variation in the renal extraction of cystatin C, these findings cast doubts on its usefulness as a glomerular filtration marker.
Received April 20, 2005
Accepted December 28, 2005
Original Article
Renal extraction of cystatin C vs 125I-iothalamate in hypertensive patients
Lyonne K. van Rossum 1 *,
Robert Zietse 2,
Arnold G. Vulto 1,
and
Yolanda B. de Rijke 3
2 Department of Internal Medicine, Erasmus MC, Dr Molewaterplein 40, 3015 GD Rotterdam, The Netherlands
3 Department of Clinical Chemistry, Erasmus MC, Dr Molewaterplein 40, 3015 GD Rotterdam, The Netherlands
Lyonne K. van Rossum, E-mail: l.vanrossum{at}erasmusmc.nl
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