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Reply to: No correlation between estimated and actual glomerular filtration rates in pediatric oncology patients

To the Editor: We appreciate the letter by Uzunova et al. in which they comment on our recent publication [1]. Uzunova et al. report a lack of agreement between the measured glomerular filtration rate (GFR) and four estimates of the GFR for 79 episodes in 29 children with cancer receiving chemotherapy [1]. They conclude that there is no significant positive correlation between estimated and actual GFR in their cohort, and even less reliability for children weighing less than 10 kg. They state that the tested estimation formulae for GFR are not safe for use in children with cancer receiving chemotherapy. Our data indicate a lack of agreement between three estimation formulae and the measured GFR in 174 children with cancer [2]. We found that none of the three tested formulae provided a clinically reliable estimate for GFR in our study population. We also found particular subsets of patients at greatest risk for overestimation of the GFR when evaluating the most clinically relevant Revised Schwartz equation; namely, children aged 6–12 years old and those patients with a diagnosis of neuroblastoma. We concluded that the three formulae tested did not provide a clinically reliable estimate for GFR in our cohort of children with cancer. Our results, and those of Uzunova et al. describe the results of two single-center, retrospective analyses of heterogeneous populations of children with cancer. We would be interested in an analysis of children with similar diagnoses receiving a comparable treatment approach, controlling for factors such as the cumulative dose of nephrotoxic chemotherapy, antimicrobials, or other known nephrotoxic agents. We agree with Uzunova et al. that the lack of agreement among estimations and measurements of glomerular filtration in children with cancer is concerning. An appropriate bedside estimation formula for glomerular filtration is an important tool to aid with dosing of chemotherapy. These two studies underscore the need to establish a more accurate bedside estimation of glomerular filtration in children with cancer.