Comparison of 24-hour urine composition prior to and after stone removal in nephrolithiasis: a prospective observational study

BACKGROUND: To evaluate 24-hour urine composition prior to and after complete stone removal in nephrolithiasis patients to determine potential relationship between kidney stones and patient metabolic status.METHODS: A prospective observational study was performed with patient enrollment from March 2019 to August 2020. 24-hour urine samples were collected prior to stone removal and 4 weeks after double-J stent removal, and examined the following urinary parameters: volume, creatinine, sodium, calcium, uric acid, citrate, oxalate, potassium, phosphorous, magnesium, and pH value. For each parameter, pairwise t test was performed to compare samples prior to and after stone removal. The number of cases that changed from normal to abnormal or vice versa was also evaluated for each parameter. The study was registered at http://clinicaltrials.gov/ (NCT03846011).RESULTS: A total of 109 patients completed 24-hour urine collections prior to and after stone removal. The urinary calcium and phosphate levels increased significantly after s tone removal, showing a mean difference o f 0.55 mmol (P=0.015) and 2.35 mmol (P=0.001) respectively. None of the other urinary parameters demonstrated a statistically significant difference when means were compared. The percentage differences for all urinary parameters ranged from 5.4% to 14.1%. The percentages of patients that presented clinically significant changes in urinary parameter values from normal to abnormal or vice versa ranged from 4.6% to 20.1%. CONCLUSIONS: Ideally, evaluation of 24-hour urine compositions should be undertaken after total stone removal, especially for patients with calcium stones. For patients who cannot achieve total stone removal, 24-hour urine samples should be thoroughly interpreted as urinary calcium and phosphate levels might be depleted in the presence of urinary stones.