Reduced Diffusing Capacity in Humidifier Disinfectant-Associated Asthma Versus Typical Asthma: A Retrospective Case Control Study

BACKGROUND: Humidifier disinfectant-related lung injury (HDLI) is a severe form of toxic inhalational pulmonary parenchymal damage found in residents of South Korea previously exposed to specific guanidine-based compounds present in humidifier disinfectants (HD). HD-associated asthma (HDA), which is similar to irritant-induced asthma, has been recognized in victims with asthma-like symptoms and is probably caused by airway injury. In this study, diffusing capacity of the lung for carbon monoxide (DL(CO)) in individuals with HDA was compared to that in individuals with pre-existing asthma without HD exposure. METHODS: We retrospectively compared data, including DL(CO) values, of 70 patients with HDA with that of 79 patients having pre-existing asthma without any known exposure to HD (controls). Multiple linear regression analysis and logistic regression analysis were performed to confirm the association between HD exposure and DL(CO) after controlling for confounding factors. The correlation between DL(CO) and several indicators related to HD exposure was evaluated in patients with HDA. RESULT: The mean DL(CO) was significantly lower in the HDA group than in the control group (81.9% vs. 88.6%; P = 0.021). The mean DL(CO) of asthma patients with definite HD exposure was significantly lower than that of asthma patients with lesser exposure (P for trend = 0.002). In multivariable regression models, DL(CO) in the HDA group decreased by 5.8%, and patients with HDA were 2.1-fold more likely to have a lower DL(CO) than the controls. Pathway analysis showed that exposure to HD directly affected DL(CO) values and indirectly affected its measurement through a decrease in the forced vital capacity (FVC). Correlation analysis indicated a significant inverse correlation between DL(CO)% and cumulative HD exposure time. CONCLUSION: DL(CO) was lower in patients with HDA than in asthma patients without HD exposure, and decreased FVC partially mediated this effect. Therefore, monitoring the DL(CO) may be useful for early diagnosis of HDA in patients with asthma symptoms and history of HD exposure.