Cystatin C Based Equation Accurately Estimates Glomerular Filtration Rate in Children With Solid and Central Nervous System Tumours: Enough Evidence to Change Practice?

Background

Assessing the glomerular filtration rate (GFR) of paediatric patients receiving nephrotoxic chemotherapy is a vital element of clinical practice. Isotopically measured GFR is the gold standard in terms of accuracy but requires injection of tracer followed by several hours of blood tests. Estimation of GFR using creatinine is widely used but inaccurate, and there is increasing concern regarding its usage for paediatric oncology patients. Cystatin C (CysC) based equations are increasingly used in other paediatric specialities to estimate GFR, and their usefulness in paediatric oncology practice is becoming evident.

Methods

We assessed the renal function of children with solid tumours and CNS tumours receiving nephrotoxic chemotherapy over a 1-year period using paired CysC and isotopic GFR.

Results

Fifty-six sets of measurements were reviewed with estimated GFR predicted using CysC-based and creatinine-based equations. The best performing equation was the 'new CKiD' equation, which estimated GFR within 30% of the measured GFR on 86% of occasions, outperforming the Schwartz equation. If estimated GFR using this equation was >100 ml/min/1.73 m², all values of measured GFR were normal at >90 ml/min/1.73 m², a category containing two-thirds of all measurements.

Conclusions

The new CKiD equation predicts GFR in paediatric oncology patients with more accuracy than creatinine-based equations. When the estimated GFR is >100 ml/min/1.73 m², isotopic GFR can be safely omitted.

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