Monitoring renal function in children with Fabry disease: comparisons of measured and creatinine-based estimated glomerular filtration rate.

BACKGROUND Studies on renal function in children with Fabry disease have mainly been done using estimated creatinine-based glomerular filtration rate (GFR). The aim of this study was to compare estimated creatinine-based GFR (eGFR) with measured GFR (mGFR) in children with Fabry disease and normal renal function. METHODS Eighty-two examinations were done in 42 children (24 boys, 18 girls) with Fabry disease from three different centres. The mean age was 12.3 years. GFR was measured with iohexol, Cr(51)-EDTA or iothalamate, and the mean mGFR was 108 ml/min/1.73 m(2). RESULTS The widely used original Schwartz formula (1976) overestimated GFR substantially by 50.6 ml/min/1.73 m(2) with a very low accuracy, whereas the new abbreviated Schwartz formula (2009) showed relatively good performances with a mean GFR overestimation of 5.3 ml/min/1.73 m(2) and 79% of the eGFR calculated within 20% of mGFR, thus being only slightly superior to the Counahan-Barratt formula. However, less than half of the eGFR calculated by the new abbreviated Schwartz equation were within 10% of the mGFR. When repeated measurements were performed, mGFR showed less variation than eGFR. CONCLUSIONS The new abbreviated Schwartz formula should replace the original Schwartz formula in the routine follow-up of children with Fabry disease. The current creatinine-based GFR formulas are all hampered by low accuracy in the 'creatinine-blind' GFR range, and early progressive disease may be missed. Supplemental mGFR is, therefore, recommended in patients where changes in GFR have potential impact on important treatment regimens. Cystatin C-based GFR formulas remain to be validated in Fabry children.