In a study by Yonezawa et al. [18], it was reported that although the elevated MPXI indicates increased MPO activities for microbicidal activities in infectious state, because MPXI level is presumably controlled by the process of synthesising and releasing of MPO, in severe bacterial infections such as sepsis, the activated neutrophils release large amounts of MPO for bactericidal activities, and an increase in degranulated neutrophils can reduce the MPXI values. Here, MPO is linked to bacterial infectious disease.