Ishizuka et al. Allergy, Asthma & Clinical Immunology 2011, 7:15 http://www.aacijournal.com/content/7/1/15 Page 6 of 8 Figure 5 The relationship between past history of asthma and current symptoms of asthma. Overall, 17.6% of students ranging in age from 18 to 24 years had suffered from asthma. The percentage of students who had a past history of asthma was significantly greater in men (21.8%) than in women (14.2%) (p < 0.05) (A). Of the students who had suffered from asthma, 35% had current asthma symptoms. Further, 41 (7.0%) of 584 students ranging in age from 18 to 24 years had any asthmatic symptoms, including wheezing, a nocturnal feeling of tightness in the chest, a nocturnal attack of shortness of breath, or a nocturnal attack of cough, within the last year, although they did not have a past history of asthma (B). FENO was ≥ 38.0 ppb in 11 of 41 students who had any asthmatic symptoms within the last year, but did not have a past history of asthma. FENO was ≥ 38.0 ppb in 7 of 14 male students and 4 of 27 female students. The percentage of these 41 students whose FENO was ≥ 38.0 ppb was significantly greater in men than in women (p < 0.05) (C). sensitive and specific symptom for the diagnosis of asthma [21]. Although a few studies have described gen- der differences in asthmatic symptoms [22-24], a noc- turnal cough attack was observed significantly more often in women than in men in our survey as well as a previous study in Australia [22]. Less than 30% of sub- jects who had a nocturnal attack of cough had an FENO ≥ 38.0 ppb. It was even smaller when subjects were lim- ited to women. This suggests that a nocturnal cough attack as a subjective symptom is not closely related to the presence of chronic eosinophilic airway inflamma- tion that is characteristic for typical asthma. Although a cough attack disturbing sleep is also one of the impor- tant symptoms that indicates asthma [22,25], it might be risky to make diagnosis of asthma based on this symp- tom especially in women. In our study, FENO was significantly higher in men than in women aged between 18 to 24 years. Similarly, it has been reported that FENO was significantly higher in males than in females, in healthy children and healthy adults [26-29]. However, there are also some reports that deny the gender difference of FENO [30-35]. Thus, the influence of gender on FENO is still a matter of some controversy. Because gender difference in FENO was observed in our study, we tried to construct the ROC curve separately for males and females. When 44.0 ppb was used as the cut-off value for men and 37.0 ppb was for women, both sensitivity and specificity were much the same between men and women. We reanalyzed all data by using the gender-specific cut-off value to make assurance doubly sure. As a result, only one man was excluded from asthma and only one woman was included in asthma. Namely, the man who had experienced a cough attack was not considered to have asthma because his FENO was 38.4 ppb and the woman who had experi- enced wheezing was considered to have asthma because her FENO was 37.5 ppb. When we used the gender-speci- fic cut-off value, FENO levels were the cut-off value and over in 34.8% of 266 male students and 26.1% of 318 female students. The percentage was significantly greater in men than in women (p < 0.05). Therefore, the results in our study did not change so much even if we used the gender-specific cut-off value. In general, boys have a higher current prevalence of asthma than girls. This trend is reversed in adulthood, such that males have a lower prevalence than females. Actually, the percentage of students with a past history of asthma was higher in male students than in female stu- dents in our study. Gender differences in both FENO levels and a past history of asthma might mean that eosi- nophilic airway inflammation induced by prolongation of childhood asthma is currently present more in men than in women aged 18 to 24 years. Of students in this age group who had suffered from and still had asthma, only 3