- For pediatric patients, creatinine clearance greater than or equal to 90 ml/min/1.73 m2 according to the Schwartz formula for estimated GFR (ml/min/1.73m2) = k*height (cm)/serum creatinine (mg/dL). k is a proportionality constant that varies with age and is a function of urinary creatinine clearance per unit of body size; 0.45 up to 12 months of age; 0.55 children and adolescent girls; and 0.70 for adolescent boys