Proteinuria in obstructive sleep apnea

Background. Previous studies have reported an association between obstructive sleep apnea (OSA) and proteinuria, but are limited in their ability to assess proteinuria accurately, to adjust for confounders such as obesity, or to exclude confidently underlying renal disease in patients with OSA and nephrotic-range proteinuria. Methods. The spot urine protein/creatinine ratio was measured in a prospective consecutive series of 148 patients referred for polysomnography who were not diabetic and had not been treated previously for OSA. The urine protein/creatinine ratio was compared across four levels of OSA severity, based on the frequency of apneas and hypopneas per hour: <5 (absent), 5 to 14.9 (mild), 15 to 29.9 (moderate), and ≥30 (severe). Results. The median level of urine protein/creatinine ratio in all categories of OSA was <0.2 (range 0.03 to 0.69; median 0.06 in patients with normal apnea hypopnea index, 0.06, 0.07, 0.07 in patients with mild, moderate, and severe OSA, respectively). Eight subjects had a urine protein/creatinine ratio greater than 0.2. Univariate analysis showed a significant association between urine protein/creatinine ratio and older age (P<0.0001), hypertension (P<0.0001), coronary artery disease (P=0.003), and arousal index (P=0.003). Body mass index (P=0.16), estimated creatinine clearance (P=0.17), and apnea hypopnea index (P=0.13) were not associated with the urine protein/creatinine ratio. In multiple regression analysis, only age and hypertension were independent positive predictors of the urine protein/creatinine ratio (P<0.0001, R²=0.17). Conclusion. Clinically significant proteinuria is uncommon in sleep apnea. Nephrotic range proteinuria should not be ascribed to sleep apnea and deserves a thorough renal evaluation.