Assessing properties of Chronic Kidney Disease in children (CKiD) and the CKiD Under 25 years (CKiDU25) among healthy children and adolescents, it was found that although the CKiDU25 demonstrated major improvements than the CKiD equation, since the unexpected age decline has been removed, a systematic difference was still noted between healthy males and females.

• Gender-specific metadata (height and creatinine) for healthy children were collected from national growth curves and creatinine vs age curves, to calculate average CKiD and CKiDU25 values for each year of age and compare them against age-independent measured GFR of 107 mL/min/1.73 m ² .

• CKiD estimations demonstrated a steep decrease with age (1.5 mL/min/1.73 m ² /year in females and 2.0 mL/min/1.73 m ² /year in males) over the whole age range (2–20 years) and large differences between adolescent males and females.

• This age-decline artifact of the CKiD equation is solved by the CKiDU25 equation, because of the age/gender specific k-values.

• However, CKiDU25 still demonstrates a systematic higher estimation of approximately 10% in healthy males vs females over the entire age range.