Evaluation of Inflammatory Markers in a Large Sample of Obstructive Sleep Apnea Patients without Comorbidities

Abstract

Systemic inflammation is important in obstructive sleep apnea (OSA) pathophysiology and its comorbidity. We aimed to assess the levels of inflammatory biomarkers in a large sample of OSA patients and to investigate any correlation between these biomarkers with clinical and polysomnographic (PSG) parameters. This was a cross-sectional study in which 2983 patients who had undergone a polysomnography for OSA diagnosis were recruited. Patients with known comorbidities were excluded. Included patients (n = 1053) were grouped according to apnea-hypopnea index (AHI) as mild, moderate, and severe. Patients with AHI < 5 served as controls. Demographics, PSG data, and levels of high-sensitivity C-reactive protein (hs-CRP), fibrinogen, erythrocyte sedimentation rate (ESR), and uric acid (UA) were measured and compared between groups. A significant difference was found between groups in hs-CRP, fibrinogen, and UA. All biomarkers were independently associated with OSA severity and gender (p < 0.05). Females had increased levels of hs-CRP, fibrinogen, and ESR (p < 0.001) compared to men. In contrast, UA levels were higher in men (p < 0.001). Our results suggest that inflammatory markers significantly increase in patients with OSA without known comorbidities and correlate with OSA severity. These findings may have important implications regarding OSA diagnosis, monitoring, treatment, and prognosis. This trial is registered with ClinicalTrials.gov number NCT03070769.

Figure 1

Study flow chart.

Figure 2

Serum high-sensitivity CRP (hs-CRP), fibrinogen, erythrocyte sedimentation rate (ESR), and uric acid (UA) are elevated in OSA patients. (a) Serum hs-CRP is found elevated only in severe compared to mild OSA patients but not in control, mild, or moderate OSA patients. ^∗p < 0.05 versus mild group. (b) Serum fibrinogen is found elevated only in severe compared to mild OSA patients but not in control, mild, or moderate OSA patients. ^∗p < 0.05 versus mild group. (c) There were no significant differences between all groups for ESR (p > 0.05). (d) UA levels are significantly different between all groups, apart from mild versus moderate groups. ^∗p < 0.05 versus mild, moderate, and severe groups. ^∗∗p < 0.05 versus control and severe groups. ^#p < 0.05 versus control and severe groups. ^§p < 0.01 versus control, mild, and moderate groups.

Figure 3

Serum high-sensitivity CRP (hs-CRP), fibrinogen, erythrocyte sedimentation rate (ESR), and uric acid (UA) in males according to OSA (obstructive sleep apnea) severity. (a) Serum hs-CRP is found elevated only in severe compared to mild OSA patients but not in control, mild, or moderate OSA patients. ^∗p = 0.001 versus mild group. (b) Serum fibrinogen is found elevated in severe and moderate compared to mild OSA patients but not in control and mild OSA patients. ^∗p = 0.02, ^∗∗p = 0.001 versus mild group. (c) ESR levels are significantly different between all groups, apart from mild versus moderate (p = 0.98) and moderate versus severe groups (p = 0.06). ^∗p < 0.05 versus mild, moderate, and severe groups. ^∗∗p < 0.05 versus control and severe groups. ^#p < 0.05 versus control. ^§p < 0.05 versus control and mild groups. (d) UA levels are significantly elevated in severe compared to control, mild, and moderate groups. ^∗p < 0.001 versus severe group. ^∗∗p < 0.001 versus severe group. ^#p < 0.05 versus severe group. ^§p < 0.05 versus control, moderate, and severe groups.

Figure 4

Serum high-sensitivity CRP (hs-CRP), fibrinogen, erythrocyte sedimentation rate (ESR), and uric acid (UA) in females according to OSA (obstructive sleep apnea) severity. (a) Serum hs-CRP is found elevated in severe compared to control and mild OSA patients. ^∗p < 0.001 versus severe group, ^∗∗p < 0.05 versus severe group, ^#p < 0.05 versus control and mild groups. (b) serum fibrinogen is found elevated in severe compared to control and moderate OSA patients. ^∗p = 0.01 versus severe group, ^∗∗p = 0.026 versus severe group, ^#p < 0.01 versus control and moderate groups. (c) ESR levels are significantly elevated in controls compared to moderate and severe groups. ^∗p < 0.05 versus moderate and severe groups. ^∗∗p = 0.02 versus controls. ^#p < 0.001 versus controls. (d) UA levels are significantly different between all groups, apart from mild versus moderate group (p = 0.15). ^∗p < 0.05 versus mild, moderate, and severe groups. ^∗∗p < 0.05 versus control and severe groups. ^#p < 0.05 versus control and severe groups. ^§p < 0.01 versus control, mild, and moderate groups.

Figure 5

Serum high-sensitivity CRP (hs-CRP) (a), fibrinogen (b), erythrocyte sedimentation rate (ESR) (c), and uric acid (UA) (d) according to gender and OSA severity.