First, because we established a more sensitive ELISA method for serum HO-1 measurement than the commercial ELISA and validated the sensitivity of this new ELISA technique in patients with ARDS with high HO-1 production, we should examine the ability to detect serum HO-1 in patients with diseases with low HO-1 production, including COPD, UIP, and so on. Here, HMOX1 is linked to chronic obstructive pulmonary disease.