24-h urine collection in patients with urolithiasis: perspective on renal function

A prospective observational study involving consecutive patients diagnosed with symptomatic urolithiasis was conducted to evaluate the serial change of urinary protein and 24-h urine chemistry with time after surgical procedures for urolithiasis. A consecutive 24-h urine samples, including calcium, uric acid and citrate were collected before surgical treatments, 4 ~ 8 weeks after surgery and 6 months after surgery. The urinary protein to creatinine ratio was also repeated at each timepoint. Forty-seven patients completed the study. The quantity of 24-h urine chemistry, including calcium, uric acid and citrate, changed over time and tended to increase (p = 0.013, 0.076 and 0.004, respectively), but the changes were not prominent during short-term follow-up. In contrast, the urinary protein to creatinine ratio decreased (p < 0.001) after surgical treatment for symptomatic renal stones, and the change was reflected in short-term follow-up. However, the serial changes in the urinary protein to creatinine ratio were significantly related to the serial changes in the 24-h urinary chemistry (p < 0.001). Surgical decompression for symptomatic urolithiasis could decrease the urinary protein to creatinine ratio, indicating improvement from renal damage, which may be reflected in the increase in 24-h urinary chemistry, including calcium, uric acid and citrate. These results strengthen the previous guidelines for the timing of 24-h urine collection and provide new insight into the optimal timing from the perspective of renal function.