Comparison of 24-hour Collecting Urine Prior and After Stone Removal

Metabolic Evaluation of Urolithiasis: Comparison of 24-hour Collecting Urine Prior and After Stone Removal - a Prospective Study

The metabolic evaluation is crucial for determining possible underlying diseases causing stone growth and to consider the lifestyle changes or medical prophylaxis needed to prevent or at least reduce stone recurrence. 24-hour urine collection is the main part of the metabolic evaluation. The time point is suggested between 3 weeks and 3 month after stone removal, but so far there are no studies comparing 24-hour urine prior and after stone removal. In this study, investigators would like to analyze parameters in the 24-hour urine prior and after complete stone removal to see whether metabolic status can be evaluated no matter stone free or not.

Background As the metabolic evaluation is an essential part of diagnostic and recurrence prevention of urolithiasis, the current EAU Guidelines, as well as the German S2k guidelines therefore suggest 24-hour urine collection, done twice. This evaluation is crucial for determining possible underlying diseases causing stone growth and to consider the lifestyle changes or medical prophylaxis needed to prevent or at least reduce stone recurrence.

The time point is suggested between 3 weeks and 3 month after stone removal, but so far there are no studies comparing 24-hour urine prior and after stone removal. This could simplify the diagnostic and make this essential information available for more patients suffering from urolithiasis.

Hypothesis

Null hypothesis: The analyzed parameters in the 24-hour urine prior and after complete stone removal differ from each other Alternative hypothesis: The analyzed parameters in the 24-hour urine prior and after complete stone removal do not differ from each other Primary endpoint: The difference of the analyzed parameters prior and after complete stone removal

Parameters to be collected

1. 24h urine composition prior and after stone removal: pH value, spec. weight, creatinine, calcium, oxalate, uric acid, citrate, magnesium, phosphate, ammonium, cysteine, sodium, potassium.
2. Secondary: Age, sex, body mass index, stone composition analyzed by infrared spectroscopy, urine culture, comorbidities (diabetes mellitus, hypertension, …), degree of hydronephrosis, serum electrolytes, blood urea nitrogen, serum creatinine, first manifestation or recurrent disease

Methods

• After assessing inclusion and exclusion criteria, all eligible patients administered for active stone removal are included in this study.
• Prior to surgery, a 24-hour urine collection need to be performed (not longer than 2 month).
• Post-operatively stone free status is assessed by NCCT, in ureterolithiasis only if stone free status is uncertain.
• 4 weeks after proven stone free status the post surgical 24h urine collection is performed.
• If a ureter stent was placed, the 24-hour urine collection is performed 4 weeks after stent removal.
• All 24-hour collection are performed as outpatients. Patients will be asked to drink and eat normally when they do their urine collection. Urinary volume is measured as a marker of liquid consumption, sodium as a marker of salt intake.

Sample size As no available data to show the difference of urine composition prior or after surgery, the study will enroll 100 participants first to get preliminary data. Then the final sample size will be determined by the preliminary data.

Statistical Analysis： Comparisons of the urine compositions before and after stone removal will be performed using the Student's t-test for continuous variables and chi-squared for categorical variables.

Inclusion Criteria:

• Patients 18 years or older
• Urolithiasis (Nephrolithiasis, Ureterolithiasis)

Exclusion Criteria:

• Patients under 18 years
• Urinary tract infection (positive urine culture prior to surgery)
• Incomplete 24h urine collection
• Pregnancy
• Residual stones after surgery