Prevalence of asthma symptoms based on the European Community Respiratory Health Survey questionnaire and FE NO in university students: gender differences in symptoms and FE NO
© Ishizuka et al; licensee BioMed Central Ltd. 2011
Received: 16 June 2011
Accepted: 19 September 2011
Published: 19 September 2011
The fractional concentration of nitric oxide in exhaled air (FE NO) is used as a biomarker of eosinophilic airway inflammation. FE NO is increased in patients with asthma. The relationship between subjective asthma symptoms and airway inflammation is an important issue. We expected that the subjective asthma symptoms in women might be different from those in men. Therefore, we investigated the gender differences of asthma symptoms and FE NO in a survey of asthma prevalence in university students.
The information about asthma symptoms was obtained from answers to the European Community Respiratory Health Survey (ECRHS) questionnaire, and FE NO was measured by an offline method in 640 students who were informed of this study and consented to participate.
The prevalence of asthma symptoms on the basis of data obtained from 584 students (266 men and 318 women), ranging in age from 18 to 24 years, was analyzed. Wheeze, chest tightness, an attack of shortness of breath, or an attack of cough within the last year was observed in 13.2% of 584 students. When 38.0 ppb was used as the cut-off value of FE NO to make the diagnosis of asthma, the sensitivity was 86.8% and the specificity was 74.0%. FE NO was ≥ 38.0 ppb in 32.7% of students. FE NO was higher in men than in women. The prevalence of asthma symptoms estimated by considering FE NO was 7.2%; the prevalence was greater in men (9.4%) than women (5.3%). A FE NO ≥ 38.0 ppb was common in students who reported wheeze, but not in students, especially women, who reported cough attacks.
The prevalence of asthma symptoms in university students age 18 to 24 years in Japan was estimated to be 7.2% on the basis of FE NO levels as well as subjective symptoms. Gender differences were observed in both FE NO levels and asthma symptoms reflecting the presence of eosinophilic airway inflammation.
Trial registration number
Bronchial asthma is a chronic inflammatory disease characterized by reversible airway limitation and airway hyper-reactivity. Clinically, patients with asthma have repeated symptoms, such as wheeze, shortness of breath, or cough, especially at night or early morning. When we make a diagnosis of asthma, it is helpful to expect that the patients have eosinophilic airway inflammation although asthma is not always associated with eosinophilic inflammation. In recent years, the fractional concentration of nitric oxide in exhaled air (the fraction of exhaled nitric oxide, FE NO) has been used as a biomarker of eosinophilic inflammation in the airway [1–3]. In fact, FE NO is increased in asthmatic patients compared to healthy subjects . Measurements of FE NO are useful for making the diagnosis of asthma, and its sensitivity and specificity as a marker for the diagnosis are relatively high [5–8]. There are two procedures for FE NO measurements: online and offline. Exhaled gas is collected in a reservoir and subsequently analyzed for nitric oxide (NO) concentrations in offline measurements . Particularly in epidemiologic studies, offline measurement might be superior to online measurement because it is economical and makes it easy to measure a number of samples in a short time [10, 11].
Worldwide epidemiological surveys on adult asthma have been mainly performed using the European Community Respiratory Health Survey (ECRHS) questionnaire [12–17]. Asthma 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 ECRHS questionnaire are consistent with asthma, but certainly not specific for asthma. Moreover, we cannot guess the degree of eosinophilic airway inflammation in each subject based on the information obtained from a questionnaire. Therefore, we think that the combination of FENO measurements and the questionnaire about asthma symptoms might make it possible to develop a more objective estimate in epidemiological studies of asthma prevalence.
In this study, an analysis of the prevalence of asthma symptoms in university students was attempted using both the ECRHS questionnaire and FE NO measured by an offline method. Additionally, we tried to investigate the gender differences in FE NO levels and asthmatic symptoms.
The original 9 main questions containing sub-questions translated into Japanese in the Japanese version of the ECRHS a 1-page questionnaire were used in this study [18, 19]. Breath samples were obtained using an offline kit produced by the Center for Environmental Information Science (Tokyo, Japan) to measure FE NO under the same conditions as with online measurement [10, 11]. In this device, the expiratory flow rate is adjusted to 50 mL/s when subjects exhale at 1.5 kPa oral pressure after inhaling deeply. The adjustment was performed with a variable flux pump (SIBATA, Soka, Japan). A disposable paper mouthpiece and a viral and bacterial filter were connected to a plastic mouthpiece adaptor with a pressure gauge, followed by a plastic T-tube with a resistance valve and a bag reservoir for collecting exhaled gas. A 1.5-L Mylar bag (Sievers, Boulder, CO) was used for the reservoir bag. During expiration, subjects were asked to maintain a constant mouth pressure (1.5 kPa) by looking at a pressure gauge. Air exhaled in the first 5 seconds (250 mL) was discarded, and the air exhaled between 5 to 10 seconds (250 mL) was collected in the Mylar bag. Samples obtained in bags were stored at 4°C to overcome error induced by sample storage and FE NO was measured within 8 hours using a chemiluminescence analyzer (NOA 280, Sievers).
3. Statistical analysis
Statistical analysis was performed using SPSS software (SPSS Japan Inc., Tokyo, Japan). Differences in percentages between two groups were analyzed using the chi-square test, and differences in means between two groups were analyzed using Student's t-test.
1. Gender differences in FE NO and symptoms, especially wheeze and nocturnal cough attacks
2. Asthmatic symptoms in University students based on the ECRHS questionnaire
3. The prevalence of asthma symptoms based on the ECRHS questionnaire and FE NO measurement
FE NO was over 38.0 ppb in 42 (25 men and 17 women) of the 77 students who had any asthmatic symptoms. Thus, the prevalence of asthma symptoms over 1 year in Gunma University students was 7.2% of 584 students, based on our definition of a predictive FE NO and the information about symptoms obtained from the ECRHS questionnaire (Figure 4B). As a result of this analysis, the prevalence of asthma symptoms was greater in men (9.4%) than in women (5.3%).
4. Past history of asthma and current subjective symptoms
5. Nasal allergies including hay fever
Of the 584 students, 314 (53.8%) answered "Yes" to the question "Do you have any nasal allergies including hay fever?" FE NO was significantly higher in students who had any nasal allergies including hay fever than in other students (41.4 ± 32.2 ppb vs. 31.3 ± 25.4 ppb, mean ± SD, p < 0.01). The percentage of students who had any nasal allergies did not differ between men (54.9%, 146 of 266) and women (52.8%, 168 of 318).
The gold standard of asthma diagnosis is obstructive lung disease with airway reversibility, or airway reactivity confirmed by challenge testing, not history or symptoms. Information obtained from the questionnaire which only asks asthmatic symptoms and history of asthma is not enough to make diagnosis of asthma, because clinical suspicion of asthma should be confirmed by objective measures of pulmonary function . Strictly, current asthma symptoms on the ECRHS questionnaire are not equal to clinically current symptoms because this questionnaire is designed to detect asthma symptoms over 1 year. Although we must also emphasize that the ROC curve was constructed only to classify subjects of this study and that it was not constructed to help diagnose asthma, a previous study using the same offline method proposed that the optimal cut-off value of FENO was 38.0 ppb for detecting allergic airway inflammation in an adult population . This cut-off value was equal to that we used in this study.
In our survey, two symptoms, wheeze and a nocturnal attack of cough were most frequently reported. FE NO was ≥ 38.0 ppb in more than 75% of subjects who had wheeze. In those students who had experienced wheezing, the percentage whose FENO was ≥ 38.0 ppb was significantly higher in men than in women. This suggests that wheeze as a subjective symptom correlates with the presence of chronic eosinophilic airway inflammation especially in men. In fact, wheeze is the most sensitive and specific symptom for the diagnosis of asthma . Although a few studies have described gender differences in asthmatic symptoms [22–24], a nocturnal cough attack was observed significantly more often in women than in men in our survey as well as a previous study in Australia . Less than 30% of subjects who had a nocturnal attack of cough had an FE NO ≥ 38.0 ppb. It was even smaller when subjects were limited to women. This suggests that a nocturnal cough attack as a subjective symptom is not closely related to the presence of chronic eosinophilic airway inflammation that is characteristic for typical asthma. Although a cough attack disturbing sleep is also one of the important symptoms that indicates asthma [22, 25], it might be risky to make diagnosis of asthma based on this symptom especially in women.
In our study, FE NO was significantly higher in men than in women aged between 18 to 24 years. Similarly, it has been reported that FE NO 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 FE NO [30–35]. Thus, the influence of gender on FE NO is still a matter of some controversy. Because gender difference in FE NO 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 FE NO was 38.4 ppb and the woman who had experienced wheezing was considered to have asthma because her FENO was 37.5 ppb. When we used the gender-specific cut-off value, FE NO 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 students in our study. Gender differences in both FE NO levels and a past history of asthma might mean that eosinophilic 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 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 FE NO 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 FE NO levels . In our study, many students had nasal allergy and it may affect FE NO levels [36, 37]. As expected, FE NO was significantly higher in students who had any nasal allergies including hay fever than in other students. 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 FE NO levels , most subjects were Japanese in this study.
The prevalence of asthma based on subjective asthmatic symptoms was 13.2% in university students ranging in age from 18 to 24 years when we estimated the maximum potential prevalence. The prevalence in female students 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 FE NO levels, as well as subjective asthmatic symptoms, it was 7.2%. Interestingly, the prevalence of asthma symptoms estimated by considering FE NO in men exceeded that in women by 4.1 percentage 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.
The prevalence of asthma symptoms in university students in Japan in a single year was 7.2%, estimated on the basis of FE NO levels as well as subjective asthmatic symptoms. The prevalence, based on both of these factors, was higher in men than in women. Gender differences were observed in both FE NO levels and asthma symptoms.
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.
List of abbreviations
European Community Respiratory Health Survey
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.).
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