Ishizuka et al. Allergy, Asthma & Clinical Immunology 2011, 7:15 http://www.aacijournal.com/content/7/1/15 students were treated well, and 36 students still had asthma symptoms within the last year, which suggests that this is a problem for patients in this age group. Furthermore, about two thirds of 36 students did not see a doctor at the time of our survey. We assume that at least 11 students who did not recognize themselves as having asthma probably did have asthma because their FENO levels were over 38.0 ppb and they had asthmatic symptoms within the last year. These students should be also recommended to see a doctor. There are many other factors that can influence FENO levels [9]. In our study, many students had nasal allergy and it may affect FENO levels [36,37]. As expected, FENO was significantly higher in students who had any nasal allergies including hay fever than in other stu- dents. Interestingly, gender difference was not observed in the prevalence of nasal allergy on the basis of the questionnaire. Although Asian race may be a factor which increases FENO levels [38], most subjects were Japanese in this study. The prevalence of asthma based on subjective asth- matic symptoms was 13.2% in university students ranging in age from 18 to 24 years when we estimated the maxi- mum potential prevalence. The prevalence in female stu- dents exceeded that in male students by 1.4 percentage points. When the prevalence of asthma for the last year was estimated on the basis of FENO levels, as well as sub- jective asthmatic symptoms, it was 7.2%. Interestingly, the prevalence of asthma symptoms estimated by consid- ering FENO in men exceeded that in women by 4.1 per- centage points. This indicates that prevalence of asthma may be estimated more objectively by considering both asthma symptoms and the degree of eosinophilic airway inflammation. Patients with asthma in this age group need to be adequately diagnosed and treated well. Conclusions The prevalence of asthma symptoms in university stu- dents in Japan in a single year was 7.2%, estimated on the basis of FENO levels as well as subjective asthmatic symp- toms. The prevalence, based on both of these factors, was higher in men than in women. Gender differences were observed in both FENO levels and asthma symptoms. Additional material Additional file 1: The ROC curve constructed using FENO data in university students. The ROC curve was constructed using FENO data obtained from 504 students in this study (including the samples obtained from students who were ≥ 25 years old). The asthmatic subjects included 38 students who answered that they suffered from asthma and had wheezing in the last year. The control subjects included 466 students who answered that they did not suffer from asthma and did not have 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 in the last year, and had not Page 7 of 8 experienced chronic bronchitis-like symptoms, coughing and phlegm on most days for a minimum of 3 months a year and for at least 2 successive years. List of abbreviations ECRHS: European Community Respiratory Health Survey; FENO: The fractional concentration of nitric oxide in exhaled air. Acknowledgements and Funding The authors are grateful to Dr. Akira Akasawa (National Center for Child Health and Development, Japan) and Dr. Junko Watanabe (National Hospital Organization, Sagamihara National Hospital, Japan) for permitting us to use a Japanese version of the ECRHS questionnaire. We thank Miss Hiroka Murai, a student of Gunma University School of Medicine, for her assistance on the date analysis. This work was partly supported by Health and Labour Science Research Grants (main investigator: Takahiro Tsuburai, M.D.). Author details 1Department of Medicine and Molecular Science, Gunma University Graduate School of Medicine, 3-39-15 Showa-machi, Maebashi 371-8511, Japan. 2Clinical Research Center for Allergy and Rheumatology, National Hospital Organization, Sagamihara National Hospital, 18-1 Sakuradai, Sagamihara, Kanagawa 228-8522, Japan. 3Gunma University Graduate School of Health Sciences, 3-39-15 Showa-machi, Maebashi 371-8511, Japan. 4Health and Medical Center, Gunma University, 4-2 Aramaki-machi, Maebashi 371- 8510, Japan. Authors’ contributions Intellectual planning of the project was mainly done by TI. TH, KO, KD, TT, KA, and MM participated in the design of the study. Actual experimental works were performed by TI, SM, HA, MY, and YK. TH, TT, and KA were involved in the development of methods for FENO measurements. All authors read and approved the final manuscript. Authors’ information All authors are Doctor of Medicine. TI, TH, KD, and KA are representatives of the Japanese Society of Allergology. TI, SM, TH, TT, KD, and KA are medical specialists approved by the Japanese Society of Allergology. TI is an associate professor of Gunma University Graduate School of Medicine and a clinical professor of Gunma University Hospital. SM, HA, MY and YK are research fellows in Gunma University Graduate School of Medicine. TH is an assistant professor of Gunma University Graduate School of Medicine. TT is on the faculty of Sagamihara National Hospital. KD is a professor of Gunma University Graduate School of Health Sciences. KO is a professor of Health and Medical Center, Gunma University. KA is the chief executive officer of the Japanese Society of Allergology and the director of Sagamihara National Hospital. MM is a professor of Gunma University Graduate School of Medicine. Competing interests The authors declare that they have no competing interests. Received: 16 June 2011 Accepted: 19 September 2011 Published: 19 September 2011 References 1. Taylor DR, Pijnenburg MW, Smith AD, De Jongste JC: Exhaled nitric oxide measurements: clinical application and interpretation. Thorax 2006, 61(9):817-827. 2. Rodway GW, Choi J, Hoffman LA, Sethi JM: Exhaled nitric oxide in the diagnosis and management of asthma: clinical implications. Chron Respir Dis 2009, 6(1):19-29. 3. Smith AD, Cowan JO, Brassett KP, Herbison GP, Taylor DR: Use of exhaled nitric oxide measurements to guide treatment in chronic asthma. N Engl J Med 2005, 352(21):2163-2173. 4. Kharitonov SA, Yates D, Robbins RA, Logan-Sinclair R, Shinebourne EA, Barnes PJ: Increased nitric oxide in exhaled air of asthmatic patients. Lancet 1994, 343(8890):133-135.