Severity of obstructive sleep apnea is related to C-reactive protein levels: The influence of comorbidities and self-reported sleep duration.

OBJECTIVES

To explore the association between obstructive sleep apnea (OSA) severity and C-reactive protein (CRP) levels in a large sample of patients. In addition, we investigated whether any such association between OSA and CRP could be explained by e.g., sleep duration, obesity, comorbid insomnia (COMISA), and chronic obstructive pulmonary disease (COPD).

METHODS

The sample comprised 2404 patients referred to a university hospital with suspected OSA (mean age 49.6 ± 14.0 years, 68.7 % males). All patients underwent standard out-of-centre respiratory polygraphy and completed a comprehensive questionnaire prior to the sleep study, including Bergen Insomnia Scale and self-reported sleep duration. OSA was defined as a respiratory event index ≥5. Blood samples were collected and analyzed for CRP. Pearson chi-square tests explored differences between three CRP groups (<1 mg/L; 1-3 mg/L; >3 mg/L). Logistic regression analyses with CRP >3 mg/L as dependent variable were conducted with adjustment for OSA severity, mean oxygen saturation in peripheral blood (SpO), sex, age, body mass index, and significant predictors in the crude analyses.

RESULTS

Severe OSA was an independent predictor of CRP >3 mg/L (adjusted OR = 1.70, 95 % CI 1.18-2.44). Among patients with OSA, obesity, COMISA, and COPD were associated with CRP >3 mg/L (adjusted OR = 3.64 (2.06-6.41), 1.44 (1.07-1.95), and 2.53 (1.34-4.75), respectively), compared to no such comorbidity. The association between OSA and CRP was not explained by sleep duration as neither short (<6 h) nor long (≥9 h) sleep duration were significant predictors of CRP >3 mg/L among patients with OSA.

CONCLUSION

This study showed that severe OSA, obesity, COMISA, and COPD were significant predictors of CRP >3 mg/L in a large sample of patients with OSA.