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Editor,—The study by Reeset al 1 indicates the low utility of routine glomerular filtration rate (GFR) estimation in paediatric oncology. We have performed a similar study in a regional children's cancer centre, looking at the utility of routine GFR estimation in patients who received high dose methotrexate, alkylating agents, or platinum containing cytotoxics.
The audit involved 110 GFR estimations on 42 patients, aged 5 months to 18 years, 48% of whom had haematological malignancies. The median GFR was 101 ml/kg/1.73 m2 (interquartile range 81.6 to 111.5 ml/kg/1.73 m2), with 15 measurements (13%) below 70 ml/kg/1.73 m2 (see table 1). In only two patients (4%) was treatment changed on the basis of GFR results: one was a child who had suffered mild tumour lysis syndrome, the other a young man who had previously been treated for lymphoma. Both had been exposed to amphotericin; as had eight other patients who did not require a change in management.
We also studied the relation between the ratio of height (cm):serum creatinine (μmol/l) (H:Cr ratio) to abnormal GFR results. This ratio had previously been shown to be a useful screening test for abnormal GFRs in general paediatrics,2 3 although inaccurate for estimating the absolute value.4 Setting a lower cut off of normal at 1.5 (on the basis of previously published data2) we tested this relation in 22 patients (34 measurements) who had contemporaneous height and creatinine measurements. No patients with abnormal GFR results had a H:Cr ratio greater than 1.5; the patients whose treatment had been changed had H:Cr ratios of 1.1 and 0.8. (The test had a sensitivity of 100% and specificity of 97%.)
We agree that routine estimations of GFR are unhelpful in paediatric oncology patients. The use of the H:Cr ratio is a potentially useful screening test for abnormal glomerular filtration rates.
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