Renal lithiasis in pediatric patients: correlation of methods that depend on 24-hour collections with simpler methods that do not require timed urine

Daily practice requires quick, simple and accessible methods to appropriately assess the urinary excretion of solutes in diagnostic or follow-up evaluations of children with renal lithiasis. The objective of this study was to correlate urine elimination of substances related to renal lithiasis that depend on the volume of excreted urine in a unit of time with other parameters that are calculated by measuring the concentration of these substances in blood and urine, such as urinary ratios, fractional excretions and excretion rates. The study included 401 healthy children aged 3-14 years (187 boys and 214 girls), mean age 8.78±3.40 years. The analysis was carried out by Pearson's correlation coefficient. There was significant correlation between the elimination of sodium, potassium and chlorine in 24-hour urine sample and the urinary ratios and fractional excretions of these ions. Urinary ratios and rates of excretion of calcium, uric acid, phosphate, magnesium, citrate and oxalate were highly correlated with the determinations of these substances in 24-hour collections. These equations provide relevant information for the study of the etiology of renal lithiasis in children, as well as about compliance to dietary treatment. They also assess the effectiveness of the various treatments used in these patients, without having to resort to 24-hour collections, which pose a considerable challenge in the pediatric age group.