Association between the metabolic profile of urolithiasis in children with idiopathic hypercalciuria and the composition of the stone assessed by infrared spectroscopy

Introduction
Urolithiasis is an increasingly common condition. Each patient after stone passage should have stone analysis performed. Every child with a urinary stone should be given a complete metabolic evaluation, and the stone analysis is an essential component of it. The aim of the study was to establish the relation between the metabolic profile of urolithiasis in children with idiopathic hypercalciuria and the composition of the excreted stone.

Material and methods
The study included 26 children with urolithiasis (aged 1–17 years) from whom stones were obtained for the analysis. The urine pH and the 24-hour urine excretion of calcium, phosphorus, magnesium and oxalate as well as spot urinalysis including ratio of crystalloids to creatinine from the second voided urine sample of the day were assessed. Urinary stones were analyzed by infrared spectroscopy. The relation between the metabolic data and the stone type was then analyzed, taking into account two types of minerals: stones with a predominance of calcium oxalate dihydrate (weddellite) and calcium oxalate monohydrate (whewellite).

Results
No correlation was found between the individual serum metabolic parameters of the patient and the composition of excreted stones. Substantially lower urinary excretion of phosphates, oxalate, magnesium and lower urinary pH were found in the group with predominant weddellite stones. A reduced value of each of these 4 variables increased more than sixfold the chance of diagnosing urolithiasis with stone composed of over 60% weddellite.

Conclusions
The urinary metabolic profile is associated with the composition of renal stones estimated in infrared spectroscopy in children with idiopathic hypercalciuria. The coexistence of several urinary excretion anomalies improves the prediction of the composition of the stones.