NDT Advance Access first published online on September 4, 2008
This version published online on September 5, 2008
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfn496
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Reproducibility of GFR measured by chromium-51-EDTA and iohexol
Nephrol Dial Transplant 2008; doi:10.1093/ndt/gfn499Correspondence and offprint requests to: E-mail: pierre_delanaye{at}yahoo.fr pierre_stone{at}hotmail.com
Sir,
We read with interest the article published by Bird et al. about the reproducibility of measured GFR by iohexol and Cr-51-EDTA [1]. We would like to make one comment and to share our own results on this fundamental (although understudied) topic. As we already pointed out in an NDT editorial, we share the same reserves about the opportunity to index glomerular filtration rate (GFR) with body surface area [2]. Indexing GFR with extracellular fluid volume (ECV) may be viewed as more logical as one of the major functions of the kidney is to regulate ECV. However, the fact that reproducibility of the GFR is better when indexed with ECV than when indexed with BSA is not the definite proof to use ECV indexation. The only proof would be to have an absolute correlation between GFR and ECV and that this relationship would totally disappear between indexed GFR and ECV [2]. For these reasons, we think that reproducibility of GFR measurement must be calculated from absolute, non-indexed GFR. Can Bird et al. give the reproducibility of their non-indexed GFR?
We have recently published our data regarding the reproducibility of serum creatinine and cystatin C with concomitant measurement of GFR [3]. Briefly, we have simultaneously measured GFR using the plasma clearance of iohexol and Cr-51-EDTA after 120 and 240 min as described by Brochner-Mortensen within a 1-week interval [4]. Our results in 12 healthy and fasting subjects show a slightly better reproducibility for iohexol (4.5%) than for Cr-51-EDTA (7.4%). Comparing to the Bird et al.'s results, our data show relatively the same reproducibility for GFR measured with Cr-51-EDTA (and are somewhat similar to results published previously with 51Cr-EDTA plasma clearances (9.0 ± 5.3%) [5]), although the reproducibility of GFR measured with iohexol is better. Discrepancies between the results can be explained in part by differences in the methodology of the studies. What is of interest is that we have measured iohexol with an HPLC method. This method is probably more precise than the method used by Bird et al., namely X-ray fluorescence. From an analytical point of view, the HPLC method has been strongly and deeply validated (E. Cavalier, submitted), including the low values (40–600 µg/ml), which are routinely measured. In this range, the method used by Bird et al. seems less precise [6] and, in any case, has not been validated in their Figure 1 (notably, the intercept in this figure is far from negligible). ‘Analytically’ speaking, iohexol concentrations of <600 µ g/ml are not precise enough to be used in the study by Bird et al. From our experience, such a level of concentration can be reached with the methodology used in this study (injection of 20 ml Omnipaque® 300). As analytical variance is included in the global reproducibility, this point must be underlined and can explain the better reproducibility observed using the ‘HPLC’ iohexol in our data.
Conflict of interest statement. None declared.
1 Department of Nephrology 2 Department of Clinical Chemistry University of Liège, CHU Sart Tilman, Liège, Belgium 3 Department of Physiology University of Paris 5 René Descartes, HEGP AP-HP, Paris France
References
- Bird NJ, Peters C, Michell AR, et al. Reproducibilities and responses to food intake of GFR measured with chromium-51-EDTA and iohexol simultaneously and independently in normal subjects. Nephrol Dial Transplant (2008) 23:1902–1909.
[Abstract/Free Full Text] - Delanaye P, Radermecker RP, Rorive M, et al. Indexing glomerular filtration rate for body surface area in obese patients is misleading: concept and example. Nephrol Dial Transplant (2005) 20:2024–2028.
[Free Full Text] - Delanaye P, Cavalier E, Depas G, et al. New data on the intraindividual variation of cystatin C. Nephron Clin Pract (2008) 108:c246–c248.[CrossRef][Web of Science][Medline]
- Brochner-Mortensen J. A simple method for the determination of glomerular filtration rate. Scand J Clin Lab Invest (1972) 30:271–274.[Web of Science][Medline]
- Froissart M, Rossert J, Jacquot C, et al. Predictive performance of the modification of diet in renal disease and Cockcroft–Gault equations for estimating renal function. J Am Soc Nephrol (2005) 16:763–773.
[Abstract/Free Full Text] - Brandstrom E, Grzegorczyk A, Jacobsson L, et al. GFR measurement with iohexol and 51Cr-EDTA. A comparison of the two favoured GFR markers in Europe. Nephrol Dial Transplant (1998) 13:1176–1182.
[Abstract/Free Full Text]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  P. Delanaye, C. Mariat, E. Cavalier, and J.-M. Krzesinski Errors induced by indexing glomerular filtration rate for body surface area: reductio ad absurdum Nephrol. Dial. Transplant., December 1, 2009; 24(12): 3593 - 3596. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||