Circulating C-reactive protein levels in patients with suspected obstructive sleep apnea

STUDY OBJECTIVES: To assess determinants of C-reactive protein (CRP) in a cohort of patients referred for investigation of obstructive sleep apnea (OSA) and to determine whether the overlap of OSA and chronic obstructive pulmonary disease (overlap syndrome) is associated with higher levels of CRP. METHODS: This was a cross-sectional study that included 2,352 patients seen at the West Australian Sleep Disorders Research Institute between 2006 and 2010. All patients had circulating CRP levels measured and spirometry performed. OSA was defined as an apnea-hypopnea index ≥ 5 events/h, and chronic obstructive pulmonary disease was defined as a forced expiratory volume in 1 second/forced vital capacity ratio < 0.70 and age > 40 years. Univariate and multivariate regression analysis were used to identify CRP determinants. RESULTS: The mean age was 51 years (60% male), the median apnea-hypopnea index was 27 events/h, the median 3% oxygen desaturation index was 24 events/h, the mean forced expiratory volume in 1 second was 88% predicted, and the median CRP was 3.0 mg/L. In multivariate analyses, age, body mass index, female sex, neck circumference, apnea-hypopnea index, and desaturation markers (nadir and mean oxygen saturation) were independently associated with higher CRP. Spirometric variables were not predictors. There was no significant difference in CRP among patients with OSA with or without coexisting chronic obstructive pulmonary disease. CONCLUSIONS: Markers of OSA severity (apnea-hypopnea index and oxygenation), age, body mass index, neck circumference, and female sex were independent predictors of circulating CRP levels. OSA overlapping with chronic obstructive pulmonary disease was not associated with increased CRP compared to either condition alone, suggesting other mechanisms for the increased cardiovascular disease risk in overlap syndrome. Recognizing factors that predict CRP will help identify patients at higher risk of cardiovascular disease and aid risk stratification. CITATION: Shah A, Mukherjee S, McArdle N, Singh B, Ayas N. Circulating C-reactive protein levels in patients with suspected obstructive sleep apnea. J Clin Sleep Med. 2022;18(4):993–1001.