While our study indicates that the P/L is a simple and useful biomarker for predicting in-hospital mortality in patients with COPD exacerbation and type II respiratory failure, bearing in mind the current limited evidence, we suggest that results of the P/L alone should be explained with caution and best used in conjunction with traditional inflammatory maker such as CRP to ensure better prognostic accuracy. This evidence concerns the gene CRP and chronic obstructive pulmonary disease.