GFR can be estimated from serum creatinine (Cr) in pediatric patients using prediction equations that take into account the patient’s height, age, and gender. Among the various prediction formulas that have been developed, the P-gp inhibitor Schwartz formulas are the most widely used (Eq. 1). However, the original Schwartz equation is based on serum Cr determined by the Jaffe method. This equation may overestimate the GFR if serum Cr is determined by the enzymatic method. Therefore, serum Cr should be converted before adopting the Schwartz equation. To convert serum Cr measured by the enzymatic method to that measured

by the Jaffe method, Eq. 2 can find more be used. Equation 3 is the new Schwartz equation and is an updated equation used to calculate GFR utilizing the enzymatic method. However, the revised formula still overestimates GFR when applied to Japanese children. This may be due to differences in body mass and body height between Japanese and Western children. Recently, the Committee of Measures for CKD in children of the Japanese Society of Pediatric learn more Nephrology established a new formula by measuring inulin clearance in Japanese children aged 2–11 years (Eq. 4, Table 12). Table 12 Constant k for the Schwartz formula Age Constant k (gender) 1 week Premature infants 0.33 (male and female) Term infants 0.45 (male and female) 2 weeks–1 year 0.45 (male and female) 2–12 years 0.55 (male and female)

13–21 years 0.70 (male) mafosfamide 0.55 (female) 3. Reference serum creatinine   Although serum Cr is the most commonly used marker for kidney function, serum Cr is affected by factors other than GFR, principally Cr production, which is related to body size and muscle mass. This leads to considerable variability between children of different ages and a relatively wide range of serum Cr levels

in normal individuals. Therefore, the Committee of Measures for CKD in Children of the Japanese Society of Pediatric Nephrology established a normal reference value of serum Cr for healthy Japanese children in 2011 (Table 13). Table 13 Serum Cr distribution in healthy Japanese children (enzymatic method) Age 2.50 % 50.00 % 97.50 % 3–5 (months) 0.14 0.2 0.26 6–8 0.14 0.22 0.31 9–11 0.14 0.22 0.34 1 (year) 0.16 0.23 0.32 2 0.17 0.24 0.37 3 0.21 0.27 0.37 4 0.2 0.3 0.4 5 0.25 0.34 0.45 6 0.25 0.34 0.48 7 0.28 0.37 0.49 8 0.29 0.4 0.53 9 0.34 0.41 0.51 10 0.3 0.41 0.57 11 0.35 0.45 0.58 Age (years) Male Female 2.50 % 50.00 % 97.50 % 2.50 % 50.00 % 97.50 % 12 0.4 0.53 0.61 0.4 0.52 0.66 13 0.42 0.59 0.8 0.41 0.53 0.69 14 0.54 0.65 0.96 0.46 0.58 0.71 15 0.48 0.68 0.93 0.47 0.56 0.72 16 0.62 0.73 0.96 0.51 0.59 0.74 For children aged 2–11 years, the reference serum Cr level can be estimated using a simple equation (Eq. 5).