Modification of the Schwartz equations for children increases their accuracy at eGFR > 60 mL/min/1.73 m(2)

Aim: Estimation of eGFR in children with normal kidney function using the Schwartz equations results in underestimating real GFR.

Materials and methods: We propose modification of three Schwartz equations - two based on creatinine concentration (eGFRScrBS bedside) and (eGFRScr) and one 3-marker based on creatinine, urea and cystatin C concentrations (eGFRS3M). The iohexol test (reference method) was performed 417 times in 353 children >2 years with mean GFR: 98 ± 31.6 ml/min/1.73m(2). The assessment included also the Filler and Zappitelli equations. The modification was performed using methods: (1) based on equation, eGFRcor = a [eGFR - T] + T, where T = 50, if eGFR > T, and a equals for: eGFRScrBS 1.4043, for eGFRScr 2.0048, for eGFRS3M 1.2951, and (2) based on correction of all coefficients of the original equation.

Results: For comparison of all the results and for children with GFR< 60, 60-90, 90-135 and > 135 ml/min/1.73m(2) the correlation coefficient, relative error (RE) and root mean square relative error (RMSRE) was employed and revealed improvement of RE from 25.9 to 6.8 and 3.9% (depending on the correction method) for eGFRScr; from 19 to 8.1 and 3.9% for eGFRScrBS and: from 11.6% to 2.0 and 2.3% for eGFRS3M (respectively). The RMSRE values changed from 30 to 21.3 and 19.8% for eGFRScr, from 25.1 to 21.6 and 19.8% for eGFRScrBS and from 19.1 to 15.8 and 15.3 % for eGFRS3M.

Conclusions: Modifications of Schwartz equations at GFR > 60 ml/min/1.73m(2) significantly improves the accuracy of calculating eGFR. The 3-markers equation is more accurate and should be employed frequently.