[Identification of lithogenic risk factors by a simplified first-line laboratory assessment in urinary calculi patients].

Introduction: A simplified first-line laboratory assessment is recommended by the Stones Committee of the Association Française d'Urologie (CLAFU) right from the first episode of renal stones to detect any lithogenic risk factors. This study was designed to evaluate the feasibility of this assessment in urology, to specify the frequency of risk factors and to compare the results between first stone formers and recurrent stone formers.
Material and Methods: This prospective study included patients with a first stone or recurrent stones with no previous laboratory assessment. Known cases of secondary stones were excluded. The stone or fragments had to be analysed by infrared spectrophotometry. In addition to the usual assessment, the first-line laboratory assessment was performed two to three months after the acute episode with a blood test (calcium, phosphorus, uric acid and creatinine), 24-hour urine collection (volume, calcium, uric acid, urea, creatinine, sodium) and first morning urine sample (pH, density, crystals).
Results: The results are based on 115 of the 204 patients included (69 first stones, 46 recurrent stones). The assessment was performed and interpreted easily, except for collection of stone fragments. Infrared spectrophotometry was performed in only 49 patients. Whewellite was the most frequent crystalline structure. No patients presented hyperparathyroidism or renal failure. In 69% of cases, the urinary assessment identified one or several risk factors, with insufficient diuresis (42%), hypercalciuria (29%), hypernatriuria (41%), high urinary urea (29%), and hyperuricuria (20%). 25% of patients had a single abnormality, 20% had two abnormalities, the most frequent combination being hypercalciuria-hypernatriuria, and 11% had 4 or more abnormalities. Comparison of first stone formers and recurrent stone formers did not reveal any difference in the frequency of lithogenic risk factors.
Conclusion: This easy to perform assessment identified lithogenic risk factors in many cases, in both first stone formers and recurrent stone formers, that can guide the prevention of recurrent stones.