Comparison of the glomerular filtration rate in children by the new revised Schwartz formula and a new generalized formula

Abstract

The most widely used formula for estimating glomerular filtration rate (eGFR) in children is the Schwartz formula. It was revised in 2009 using iohexol clearances with measured GFR (mGFR) ranging between 15 and 75 ml/min × 1.73 m(2). Here we assessed the accuracy of the Schwartz formula using the inulin clearance (iGFR) method to evaluate its accuracy for children with less renal impairment comparing 551 iGFRs of 392 children with their Schwartz eGFRs. Serum creatinine was measured using the compensated Jaffe method. In order to find the best relationship between iGFR and eGFR, a linear quadratic regression model was fitted and a more accurate formula was derived. This quadratic formula was: 0.68 × (Height (cm)/serum creatinine (mg/dl))-0.0008 × (height (cm)/serum creatinine (mg/dl))(2)+0.48 × age (years)-(21.53 in males or 25.68 in females). This formula was validated using a split-half cross-validation technique and also externally validated with a new cohort of 127 children. Results show that the Schwartz formula is accurate until a height (Ht)/serum creatinine value of 251, corresponding to an iGFR of 103 ml/min × 1.73 m(2), but significantly unreliable for higher values. For an accuracy of 20 percent, the quadratic formula was significantly better than the Schwartz formula for all patients and for patients with a Ht/serum creatinine of 251 or greater. Thus, the new quadratic formula could replace the revised Schwartz formula, which is accurate for children with moderate renal failure but not for those with less renal impairment or hyperfiltration.

Modification of the Schwartz equations for children increases their accuracy at eGFR > 60 mL/min/1.73 m2

“…[1][2][3][4][5][6][7][8][9][10][11][12] In addition to creatinine concentration, cystatin C have become increasingly more common and is supposed to be a better marker of kidney function 9,[13][14][15]16 although contrary opinions have been also expressed. 17,18,19 Also multi-marker formulas have become well known as they are believed more accurate.…”

“…Validating these equations in children with normal kidney function is considered necessary. 20,24,25 The 2009 shortened equation of Schwartz has been evaluated in children with high GFR values, 1,4,12,[26][27][28] but only isolated papers estimated the accuracy of the tri-marker equation. 29 Chehade et al…”

New Combined Serum Creatinine and Cystatin C Quadratic Formula for GFR Assessment in Children

“…To facilitate physicians' use of this new combined SCreat and CysC quadratic formula in daily care practice, we have developed a JavaScript application that can be downloaded for free (http://www.chuv.ch/combinedquadraticformula); the previously published SCreat quadratic equation (9) link can also be found at this site.…”

“…This linear model achieved accuracies within 10% and 30% of the observed values of 49% and 90%, respectively, compared with 45% and 88%, respectively, with the 0.413 Schwartz coefficient formula. Second, we fit the relationship between iGFR and the variable ratio of Ht/SCreat in a quadratic model, as proposed by Gao et al (9), as follows: iGFR = a + b(Ht/SCreat) + g(Ht/SCreat) 2 + a(age) + b(sex). We obtained a better model performance than the one obtained from the linear model, with 93% of eGFR values being within 30% of iGFR values and a highly significant (P,0.001) likelihood ratio test between these two models ( Table 3).…”

“…Likelihood ratio tests were performed to compare the fit of the combined SCreat and CysC-based logarithmic Schwartz model and the combined SCreat and CysC-based quadratic model. The cutoff of the applicability of the new combined Schwartz formula was determined by applying the circular binary segmentation method (9,13,14) to formula residuals. The circular binary segmentation method allows segmenting of data through change-point detection using a likelihood ratio statistic, which tests the null hypothesis that there is no change, against the alternative hypothesis that there is exactly one change at each location.…”