RENAL URIC ACID CLEARANCE AND EXCRETION DURING CHILDHOOD

Abstract

Quantitation of uric acid (UA) excretion and clearance (CUA) are essential when evaluating patients with abnormal serum UA or UA crystalluria. Normal values for 24 hour urinary UA excretion and CUA during childhood, however, have not been reported. We measured total UA excretion, CUA and serum UA in 52 healthy children ages 2-14 years in whom creatinine clearance (CCr) was normal and urine Na > 20 mEq/l. We found a linear increase in total UA excretion and serum UA and a linear decrease in CUA/l. 73 m2 and UA excretion mg per kg body weight with increasing age. Denoting any of these variables as y and age in years as x and correlation coefficient between x and y as r, we found: 95% confidence belts were established for each variable. Although total UA excretion increases with age, mean UA excretion per kg is greater in younger children and falls to upper adult norms (10 mg/kg) by age 10. Mean CUA/1.73 m2 is higher than adult norms (8-12 ml/min/1.73 m2) until age 7. Although filtered urate increases (serum UA increases, CCr/1.73 m2 is constant), CUA/1.73 m2 decreases with age. We conclude that tubular changes, either decreasing secretion or increasing reabsorption of UA, occur during childhood.