Methylene blue decreases the functional activity of alpha-1-protease inhibitor in bronchoalveolar lavage.

Methylene blue, used as an external marker for bronchoalveolar lavage (BAL) in a concentration of 1 microgram/ml, reduced the functional activity of BAL alpha 1-protease inhibitor (alpha 1-PI) in 2 healing nonsmokers who each had 2 BAL done, one with and the other without methylene blue. Inactivation of alpha 1-PI by methylene blue was confirmed by in vitro experiments on diluted serum and concentrated BAL incubated with methylene blue. Inactivation of alpha 1-PI is likely due to its oxidation by methylene blue, as suggested by the in vitro protective effect of dithiothreitol, a reducing agent. These observations indicate a need for caution when considering the use of methylene blue as an external marker for bronchoalveolar lavage.