CRP and chronic obstructive pulmonary disease: Breyer et al. did not find any significant difference in PaO2 between different levels of CRP.[11] The key point comes from Bircan et al.’s study which found negative correlation between PaO2 and HS-CRP in control group and patient with stable COPD but not in patients with exacerbation.[19] As we see in our study and Bircan et al.’s study, PaO2 was not a valuable measurement while exacerbations and perhaps Pa- CO2 was a better tool for making decisions.