Do patients with obstructive sleep apnea have clinically significant proteinuria?

AIM

Previous studies report a high prevalence of proteinuria in patients with obstructive sleep apnea syndrome (OSAS). This common syndrome may therefore be an important cause ofproteinuria and renal failure in the general population. This study was undertaken to assess the prevalence of proteinuria among OSAS patients, and to identify the factors associated with urine protein excretion in these patients.

METHODS

Overnight polysomnography, urine protein to creatinine ratio (PTCR), body mass index (BMI), mean arterial pressure (MAP), and hematocrit were assessed prospectively in 224 patients referred for evaluation of suspected OSAS. Sleep apnea was defined as apnea-hypopnea score (AHS) > or = 5 events/hour. Proteinuria was defined as PTCR > 0.2 mg/mg.

RESULTS

Sleep apnea was present in 143 subjects (63.8%), and proteinuria in 10 (4.5%). The highest PTCR was 0.677 mg/mg. PTCR and AHS were weakly correlated (r = 0.12, p = 0.08). PTCR correlated (alpha = 0.05) with lowest oxygen saturation (r = -0.18, p = < 0.01), time spent with oxygen saturation below 90% (r = 0.19, p = < 0.01), and BMI (r= 0. 17, p = < 0.01). The mean PTCR was similar in subjects with and without sleep apnea. Proteinuria was present in 7 of 143 (4.9%) subjects with AHS > or = 5 and 3 of 81 (3.7%) subjects with AHS < 5, a relative risk of 1.34, 95% CI (0.34, 5.32). Predictors of LogPTCR in multiple linear regression (model R2 - 0.104) were: AHS (< 5 or > or = 5), baseline oxygen saturation, sex, and MAP.

CONCLUSIONS

Clinically significant proteinuria is uncommon in OSAS. The prevalence and severity of proteinuria are similar in both OSAS patients and patients without sleep-disordered breathing. Sleep apnea severity is weakly associated with urine protein excretion, related more to hypoxemia than to frequency of apneic events.