Estimating glomerular filtration rate (GFR) in children. The average between a cystatin C- and a creatinine-based equation improves estimation of GFR in both children and adults and enables diagnosing Shrunken Pore Syndrome.

Estimating glomerular filtration rate (GFR) in adults by using the average of values obtained by a cystatin C- (eGFR _{cystatin C} ) and a creatinine-based (eGFR _creatinine ) equation shows at least the same diagnostic performance as GFR estimates obtained by equations using only one of these analytes or by complex equations using both analytes. Comparison of eGFR _{cystatin C} and eGFR _creatinine plays a pivotal role in the diagnosis of Shrunken Pore Syndrome, where low eGFR _{cystatin C} compared to eGFR _creatinine has been associated with higher mortality in adults. The present study was undertaken to elucidate if this concept can also be applied in children. Using iohexol and inulin clearance as gold standard in 702 children, we studied the diagnostic performance of 10 creatinine-based, 5 cystatin C-based and 3 combined cystatin C-creatinine eGFR equations and compared them to the result of the average of 9 pairs of a eGFR _{cystatin C} and a eGFR _creatinine estimate. While creatinine-based GFR estimations are unsuitable in children unless calibrated in a pediatric or mixed pediatric-adult population, cystatin C-based estimations in general performed well in children. The average of a suitable creatinine-based and a cystatin C-based equation generally displayed a better diagnostic performance than estimates obtained by equations using only one of these analytes or by complex equations using both analytes. Comparing eGFR _cystatin and eGFR _creatinine may help identify pediatric patients with Shrunken Pore Syndrome.