The impact of body mass index on quantitative 24-h urine chemistries in stone forming patients: a systematic review and meta-analysis.

To study the impact of body mass index (BMI) on quantitative 24-h urine chemistries in stone forming patients and to explore how overweight and obesity contribute to urolithiasis. A systematic search of PubMed, EMBASE, Cochrane Library, and Web of Science was performed in July 2017 and updated in October 2017 to detect relevant studies. After that, we screened all the relevant articles in accordance with the predetermined inclusion and exclusion criteria. Data of eligible studies were extracted, and then, a meta-analysis was conducted via RevMan 5.3 software. Nine studies, involving 5965 stone forming patients who underwent 24-h urine collection for chemistry analysis, were included in our analysis. BMI was used to clarify the body size. BMI ≥ 25 kg/m2 group, including overweight and obesity patients, erected more calcium (WMD 34.44 mg; 95% CI 11.33-57.55; p = 0.003), oxalate (WMD 3.44 mg; 95% CI 1.40-5.49; p = 0.001), urate (WMD 97.71 mg; 95% CI 63.05-132.38; p < 0.00001), and sodium (WMD 26.64 mg; 95% CI 18.23-35.05; p < 0.00001) in 24 h than BMI < 25 kg/m2 group. However, the BMI < 25 kg/m2 group showed higher pH of urine (WMD 0.12; 95% CI 0.04-0.20; p = 0.004). There was no significant difference in 24-h urine volume (WMD - 29.30 ml; 95% CI - 122.03 to - 63.42; p = 0.54), citrate (WMD - 34.03 mg; 95% CI - 72.88 to 4.82; p = 0.09), magnesium (WMD - 4.50 mg; 95% CI - 10.48 to 1.48; p = 0.14), phosphate (WMD - 89.38 mg; 95% CI - 219.23 to 40.47; p = 0.18), and creatinine (WMD - 191.98 mg; 95% CI - 395.35 to 11.38; p = 0.06) between the two groups. All the results kept the same tendency when gender was taken in consideration. Sensitivity analysis generated similar results. The current evidence suggested that patients with BMI ≥ 25 kg/m2 erected more promotions but not inhibitors of urolithiasis than those with BMI < 25 kg/m2, which increased the risk of urolithiasis in overweight and obesity individuals.