Twenty-four hour urine parameters in nephrolithiasis patients with obstructive sleep apnea syndrome

Objective: To study 24-hour urine metabolic abnormalities in patients with obstructive sleep apnea syndrome (OSAS), diagnosed by polysomnography. The purpose was to identify whether OSAS is independently associated with a distinctive set of 24-hour urine studies in a cohort of stone formers. Patients and Methods: Using our institutional stone database (2013–2017), 1132 consecutive patients with 24-hour urine collections were identified. After applying our exclusion criteria, the final cohort consisted of 376 patients of which 45 patients had OSAS. Descriptive statistics were used to compare 24-hour urine parameters between patients with and without OSAS. Logistic regression models were used to assess the association between OSAS and 24-hour urine parameters. Results: On univariate analysis, patients with OSAS were older (57.7 versus 48.2, p < 0.001) with a higher body mass index (BMI) (35 versus 27.8, p < 0.001), and higher likelihood of diabetes mellitus (DM) (57.8 versus 10.6%, p < 0.001) and hypertension (HTN) (60% versus 23.9%, p < 0.001). Patients with OSAS had higher 24-hour total amount of urine volume (2018 versus 1818 ml, p = 0.03), calcium (279.7 versus 208 mg, p = 0.02), oxalate (41.6 versus 31.3 mg, p < 0.001), yet lower 24-hour urine pH (5.75 versus 6.03, p = 0.001). On multivariable linear regression analysis, OSAS did not affect any of the 24-hour urinary parameters. Conclusion: OSAS is a prevalent comorbidity among nephrolithiasis patients. We found no major differences in 24-hour urine parameters between nephrolithiasis patients with OSAS and those without OSAS. Further study is needed to determine whether the severity of OSAS and compliance with treatment play a role in the pathogenesis of stone formation. Level of evidence: 2b