| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Letters to the Editor |
Department of Medicine University of Bonn, Germany
aAddress correspondence to this author at: Department of Internal Medicine I University of Bonn Sigmund-Freud-Straâe 25 D 53105 Bonn, Germany Fax +49-228-2871-4952 E-mail dr.poege{at}nephrologie-bonn.de
To the Editor:
Because we recently introduced beta-trace protein (BTP) for estimating glomerular filtration rate (GFR) in patients after kidney transplantation (1), we read with interest the report by White and coworkers (2). These authors proposed a BTP-based equation to calculate GFR in renal transplant recipients. Because a separate second cohort was not available in the reported study, a validation of the BTP-based formula was not performed. However, we were able to validate the suggested equation in 85 kidney transplant recipient patients who had participated in our study mentioned above.
The following equation of White and coworkers was applied:
 |
Correlation coefficients of the predicted GFRs by both formulae with the measured reference GFRs were high and did not differ significantly (BTP formula, r = 0.866 vs MDRD equation, r = 0.863). Both equations overestimated measured GFR to a small but significant extent [mean GFR estimated by the BTP formula was 46.7 (95% CI, 43.0–50.4) mL/min/1.73 m2 vs the mean GFR estimated by the MDRD equation, which was 45.3 (95% CI, 41.1–49.6) mL/min/1.73 m2; P < 0.001 for both]. The bias of the MDRD equation was somewhat lower than that of the BTP formula (6.7 vs 8.1 mL/min/1.73 m2, not significant). Precision (measured as SD of the mean difference between measured and estimated GFR) (6) tended to be better for the BTP formula (8.44 vs 10.03 mL/min/1.73 m2), but this difference in precision did not quite reach statistical significance (P = 0.058). The rates of predicted GFRs within 10%, 30%, and 50% of the measured GFR were comparable (BTP formula: 24.7%, 63.5%, and 84.7%, respectively, vs MDRD equation: 24.7%, 71.8%, 87.1%; not significant by McNemar test). Bland and Altman plots of the measured vs predicted GFRs of both equations are given in Fig. 1
.
|
In conclusion, this external validation provides evidence that the performance of the BTP formula suggested by White and coworkers (2) is comparable to that of the reexpressed MDRD equation. Nevertheless, some difficulties were associated with the validation process and may have affected our results: (a) the validation cohort was relatively small, (b) although the same BTP determination technique was used, no international standardization was available, (c) differences in methods used for creatinine determination were corrected mathematically but no samples were sent to the Cleveland Clinical Laboratory for analysis, and (d) the cohorts appeared to have different degrees of graft function [mean (SD) GFR 59 (23) in the patient cohort of White vs 38.6 (15.1) in our patient cohort].
Finally, an additional economic aspect must also be taken into account: BTP is considerably more expensive than creatinine. Thus, the suggested BTP-based equation for GFR calculation will gain public recognition only when its perfomance is demonstrated to be clearly superior to the MDRD equation. Further studies are needed to elucidate this issue more clearly.
Acknowledgments
Grant/Funding Support: None declared.
Financial Disclosures: None declared.
References
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
