Comparative studies to evaluate serum levels of c-reactive protein in obstructive sleep apnea and healthy controls

Aims

1. To evaluate the correlation between elevated levels of C-Reactiveprotein (CRP) and obstructive sleep apnea.
2. To compare the levels of CRP with normal controls matched for age, sex, BMI, Occupation.

Methods

Study group consisted 80 subjects. Polysomnography was done for all subjects
on the basis of which 30 subjects were taken normal controls {Apnea Hypopnea
Index (AHI) <5 and Respiratory Disturbance Index(RDI)<5}. Rest of the 50
subjects were cases. (AHI >5 and RDI >5).Various clinical and polysomnographic data {viz their neck circumferences, blood pressure, Arterial pCO2, Epworth Sleepiness Scale, AHI, and the Oxygen desaturation index(ODI)} along with serum quantitative CRP were recorded and compared between the two groups.
Results: we found positive correlation between:

1. AHI and CRP independent of BMI. R value: 0.815, P value: <0.001.
2. RDI and CRP. R value: 0.815, P value <0.001
3. ODI and CRP. R value: 0.835, P value: <0.001

Area under ROC (receiver operating characteristic) curve for AHI was 1.000 with cutoff value: 5.15 to differentiate cases from controls. P value was <0.001 Area under ROC curve for CRP was 0.878 which is considered good to differentiate cases from controls with cutoff value: 0.655.
Conclusions: CRP value is marker of inflammation and cardiovascular risk was raised in
cases independent of BMI. Its association with AHI shows that severity of
OSA is positively correlated to CRP levels. CRP levels are also positively correlated to the ODI implying Hypoxia as one of the mechanisms by which
OSA induces systemic inflammation.