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NDT Advance Access originally published online on June 17, 2006
Nephrology Dialysis Transplantation 2006 21(11):3333; doi:10.1093/ndt/gfl324
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© The Author [2006]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Renal extraction of cystatin C

Email: pierre_delanaye{at}yahoo.fr

Sir,

Cystatin C is considered as a new marker of glomerular filtration rate (GFR). However, studies on its renal physiological handling are lacking [1], making the study of van Rossum et al. interesting [2]. Nevertheless, we have some comments. Firstly, as contrast injection may induce acute variation in intrarenal haemodynamics, it would be of interest to know the timing of the sampling procedure in relation to iodine injection [3]. Secondly, the authors have described large absolute and relative variations in cystatin extraction compared with iothalamate extraction. No systematic bias could be detected, and opposite ratios are observed in both kidneys of individual patients. This could be explained in part by the high analytical coefficient of variation (CVa) reported for the cystatin measurements (11.3% for 1.4 mg/l). This CVa must still be higher in the patient samples (and not the controls given by the manufacturer DAKO). The use of sodium citrate tubes is also questionable as it is never recommended in immunoassays. Performing the cystatin in triplicate will not change this limiting fact. Thirdly, the authors confirm the tubular secretion of iothalamate [4]; however, iothalamate has been used as a GFR ‘reference’ measure in most important studies [5]. We would be interested in the authors’ opinion on this topic.

Conflict of interest statement. None declared.

Pierre Delanaye1, Etienne Cavalier2, Jean Paul Chapelle2, Jean Marie Krzesinski1 and Marc Froissart3

1Department of Nephrology and
2Department of Clinical Chemistry
University of Liège
CHU Sart Tilman
Liège, Belgium
3Department of Physiology
University of Paris 5 René Descartes
HEGP AP-HP, Paris
France

References

  1. Tenstad O, Roald AB, Grubb A, Aukland K. (1996) Renal handling of radiolabelled human cystatin C in the rat. Scand J Clin Lab Invest 56:409–414.[Web of Science][Medline]
  2. van Rossum LK, Zietse R, Vulto AG, de Rijke YB. (2006) Renal extraction of cystatin C vs 125I-iothalamate in hypertensive patients. Nephrol Dial Transplant 21:1253–1256.[Abstract/Free Full Text]
  3. Nygren A, Ulfendahl HR, Hansell P, Erikson U. (1988) Effects of intravenous contrast media on cortical and medullary blood flow in the rat kidney. Invest Radiol 23:753–761.[CrossRef][Web of Science][Medline]
  4. Odlind B, Hallgren R, Sohtell M, Lindstrom B. (1985) Is 125I iothalamate an ideal marker for glomerular filtration? Kidney Int 27:9–16.[Web of Science][Medline]
  5. Levey AS, Bosch JP, Lewis JB, et al. (1999) A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Modification of Diet in Renal Disease Study Group. Ann Intern Med 130:461–470.[Abstract/Free Full Text]

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This Article
Right arrow Extract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
21/11/3333    most recent
gfl324v1
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Right arrow Articles by Delanaye, P.
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