Hypoxemia and obesity modulate plasma C-reactive protein and interleukin-6 levels in sleep-disordered breathing.

C-reactive protein (CRP) and interleukin-6 (IL-6) are pro-inflammatory proteins and important risk factors for atherosclerosis. Plasma CRP levels in snoring children may or may not be elevated. Since obesity is prevalent among snoring children and is associated with elevated CRP levels, we aimed to investigate the relative contributions of sleep-disordered breathing (SDB) and obesity to the inflammatory processes in snoring children in this prospective study. Two hundred forty-four children (mean age 8.9 +/- 3.4 years) underwent polysomnographic evaluation. CRP was measured the following morning, and plasma IL-6 levels from 111 randomly selected children were also examined. Plasma CRP and IL-6 levels were elevated in children with SDB. Log plasma CRP levels were higher in the moderate-severe SDB group (apnea/hypopnea index, AHI > or = 5) compared to the mild SDB group (AHI > or = 1 and <5; p < 0.0001) or the control group (AHI < 1; p = 0.0001). Log plasma CRP levels correlated with AHI, arousal index, relative BMI, and SpO(2) nadir (r = 0.30, p < 0.0001; r = 0.21, p = 0.002; r = 0.39, p < 0.0001, r = -0.36, p < 0.0001, respectively). Log plasma CRP levels were lower in children with SpO(2) nadir > or =90 (p < 0.0001). Sub-analysis of the 116 non-obese children in the cohort revealed similar findings. Log plasma IL-6 levels were increased in children with moderate-severe SDB compared to controls (p = 0.03) and correlated with AHI (r = 0.28, p = 0.003) and SpO(2) nadir (r = -0.24, p = 0.02). Children with SDB display significant severity-dependent increases in plasma CRP and IL-6 levels independent of obesity.