LAUSR

To the Editor Serum creatinine (Cr)-based eGFR may be used for Japanese children aged 2–18 years to evaluate renal function, measuring serum Cr by enzymatic method [1]. In clinical practice, cystatin C (cysC)-based eGFR [2] may be used for younger children. However, cysC data are not always available for retrospective epidemiologic studies or to inform common clinical practice. Consequently, we aimed to establish a Cr-based eGFR for children aged younger than 2 years, using this formula by use of a coefficient. Physiologically, kidney function gradually increases from birth, developing to reach that found in adults by about age 2 years. Previously, we reported that median normal reference values of GFR were 91.7, 98.5, 106.3, and 113.1 mL/min/ 1.73 m in children aged 3–5, 6–11, 12–17, and 18 months–16 years, respectively [3]. Therefore, we assumed that the %medians of GFR in children aged 4, 8.5, 14.5, and 24 months were 79.5, 85.4, 92.1, and 100.0%, respectively, and calculated a regression curve using a logarithmic function as follows: R = 0.107 9 ln [age (months)] ? 0.656 (Fig. 1). In other words, a ratio of reference GFR in children aged under 2 years with that in older children can be shown as R.