Exhaled Nitric Oxide
A number of studies have investigated the relationship between exhaled nitric oxide (NO) and airway inflammation in asthma. These studies have found that levels of exhaled NO are elevated in people with asthma who are not taking inhaled glucocorticosteroids compared to people without asthma, yet these findings are not specific for asthma. Exhaled NO is thought to reflect eosinophilic airway inflammation in asthma.
Levels of exhaled NO have been suggested as non-invasive markers of airway inflammation in asthma, as an alternative to invasive methods such as examination of spontaneously produced or hypertonic-saline induced sputum for eosinophils and metachromatic cells. Measurement of exhaled NO may prove to be useful in diagnosing asthma, assessing adherence to treatment with inhaled corticosteroids, or in the identification of patients in whom respiratory symptoms are associated with eosinophilic airway inflammation. A number of methods have been developed to measure exhaled NO, including laser spectroscopy and chemiluminescence.
Current studies on exhaled NO in asthma have focused on the technical feasibility of measurement and correlations with pulmonary function and invasive methods of assessing airway inflammation. The evidence for assessment of exhaled NO for other pulmonary conditions is more limited. However, well-designed, long-term studies are needed to evaluate whether the addition of exhaled NO measurements to clinical and lung function assessment results in improved asthma control.
An assessment on a NO measurement system (NIOX) for monitoring response to asthma treatment prepared by the Canadian Coordinating Office for Health Technology Assessment (CCOHTA) (Hailey, 2004) concluded that no information was found on the extent to which the use of this device improves patients' compliance with medication use or ensures appropriate prescribing. Comparative studies to obtain such measures of efficacy would be desirable. This is in agreement with the observation of Zeidler et al (2004) who stated that exhaled NO may be a useful parameter for monitoring asthmatic inflammation, adjusting therapy, and diagnosing asthma, although prospective longitudinal trials investigating the correlation between exhaled NO and clinical outcomes are necessary to determine its utility.
An assessment by the BlueCross BlueShield Association (BCBSA) Technology Evaluation Center (TEC) (2006) concluded that use of exhaled NO (FENO) levels for monitoring patients with chronic asthma does not meet the TEC criteria. The TEC assessment found that available evidence does not permit the conclusion that use of FENO monitoring to guide treatment decisions in asthma leads to improved outcomes. The assessment stated that the 7 studies that evaluated the predictive ability of FENO, and its potential to provide prognostic information that could influence management decisions, had considerable methodologic limitations and variability in study methodology that precluded synthesis of their results and definitive conclusions. The assessment stated that the 2 randomized, controlled trials included in the review suggest possible benefits for FENO monitoring, but are not sufficient to conclude that outcomes are improved. The assessment explained that each study reported different benefits that have not been reproduced. The assessment noted that differences in the control management strategy raise questions about the optimal management strategy to which FENO monitoring should be compared.
In a randomized-controlled trial, Smith et al (2005) reported a reduction in use of inhaled corticosteroids in asthma patients (n = 46) using FENO measurements to adjust their doses compared to asthma patients (n = 48) using conventional guidelines to adjust their doses. Patients were followed for 12 months. The final mean daily doses of fluticasone were 370 µg for the FENO group versus 641 µg for the control group, a difference of 270 µg per day. The rates of exacerbation were 0.49 episodes per patient in the FENO group and 0.90 in the control group, representing a non-significant reduction of 45.6 % in the FENO group. The authors reported no significant differences in other markers of asthma control, use of oral prednisone, pulmonary function, or levels of airway inflammation (sputum eosinophils). Earlier studies, however, have demonstrated that control can be maintained through a standardized approach involving a uniform dose reduction. Smith’s findings may reflect over treatment in the control group rather than more appropriately targeted treatment in the FENO group. It is also unclear what effects multiple medications may have on the relationship between asthma control and FENO measurements.
van Mastrigt et al (2007) stated that there is still much uncertainty about the potential clinical utility of measurement of fractional FENO in infants. There is a need for clinical studies showing the merits and limitations of different methodologies, to standardize measurements of fractional FENO in infants, and to obtain normal reference values for this age group. Turner (2007) stated that over a relatively short time FENO has become recognized as an useful objective tool for diagnosing and monitoring asthma. However, more clinical studies are needed in order for FENO to become fully established in the diagnosis and management of asthma.
Shaw and co-workers (2007) tested the hypothesis that titrating corticosteroid dose using the concentration of FENO in exhaled breath results in fewer asthma exacerbations and more efficient use of corticosteroids, when compared with traditional management. A total of 118 subjects with a primary care diagnosis of asthma were randomized to a single-blind trial of corticosteroid therapy based on either FENO measurements (n = 58) or British Thoracic Society guidelines (n = 60). Participants were assessed monthly for 4 months and then every 2 months for a further 8 months. The primary outcome was the number of severe asthma exacerbations. Analyzes were by intention-to-treat. The estimated mean (SD) exacerbation frequency was 0.33 per patient per year (0.69) in the FENO group and 0.42 (0.79) in the control group (mean difference, -21 %; 95 % confidence interval [CI]: -57 % to 43 %; p = 0.43). Overall, the FENO group used 11 % more inhaled corticosteroid (95 % CI: -17 % to 42 %; p = 0.40), although the final daily dose of inhaled corticosteroid was lower in the FENO group (557 versus 895 microg; mean difference, 338 microg; 95 % CI: -640 to -37; p = 0.028). The authors concluded that an asthma treatment strategy based on the measurement of FENO did not result in a large reduction in asthma exacerbations or in the total amount of inhaled corticosteroid therapy used over a 12-month period, when compared with current asthma guidelines.
Travers and associates (2007) attempted to develop reference ranges for FENO and ascertained which factors in health and disease influence FENO levels. Subjects aged between 25 and 75 years were drawn from a random sample of the predominantly white population of Wellington, New Zealand. Exhaled NO was measured using an online NO monitor in accordance with international guidelines. A detailed respiratory questionnaire and pulmonary function tests were performed. The geometric mean FENO was 17.9 parts per billion (ppb) with a 90 % CI for an individual prediction (reference range) for normal subjects of 7.8 to 41.1 ppb. Sex, atopy, and smoking status significantly affected FENO levels, and several reference ranges were presented adjusting for these factors. Asthma and allergic rhinitis were associated with higher FENO. Measurement of FENO had poor discriminant ability to identify steroid-naive subjects with asthma.
Ramser and colleagues (2008) evaluated FENO as a surrogate for bronchial hyper-responsiveness (BHR) in children with possible reactive airway disease. Exhaled NO was measured using the single-breath method in 169 successive outpatients 11 +/- 5 years of age before lung function testing and subsequent bronchial provocation by exercise (n = 165) and methacholine (n = 134). Baseline forced expiratory volume in 1 second (FEV1) less than 80 % of predicted and/or BHR were seen in 59 %. Exhaled NO correlated weakly with PD(20) to methacholine (r = -0.24, p < 0.05), but not with the change in FEV1 due to exercise-induced bronchoconstriction (EIB) (r = 0.1, p > 0.05). The negative predictive value of FENO less than 10 ppb for EIB was 94 %, but overall accuracy for predicting BHR was low. The authors concluded that measurement of FENO is not a substitute for bronchial provocation in children.
A study by Szefler et al (2008) found that measurement of FENO did not improve asthma outcomes. In a randomized clinical trial, 546 adolescents and young adults with persistent or uncontrolled asthma were assigned to receive computer-protocol-driven care, with or without measurement of FENO. During the 46-week study, patients returned for visits every 6 to 8 weeks, and their medicines were adjusted as required. Mean numbers of days with asthma symptoms during the 2 weeks before each visit was similar in the NO and control groups (1.93 versus 1.89). No differences between groups were noted in secondary outcomes, including measures of pulmonary function and asthma exacerbations.
Guidelines from the National Asthma Education Program (NIH, 2007) state that NO expired gas determination is among several biomarkers that may potentially be used for asthma management in the future. The guidelines note that fractional FENO concentration is one of many biomarkers that have been proposed. "Few studies, however, have validated or 'anchored' assessment of these markers by analyzing their relationship to the rate of adverse events or decline in pulmonary function over time. Further complicating the matter is that the relationship between normalization of a biomarker and normalization of risk of an adverse event may depend on the specific treatment given. What is found true for treatment with an [inhaled corticosteroid] ICS may not be true for treatment with a leuktotriene receptor antagonist (LTRA) or an inhaled long-acting beta2-agonist (LABA), or vice versa." The guidelines concluded that, "[i]n the future, assessment of a combination of historical features and of biomarkers may allow accurate estimation of the risk of future adverse events, but it must be kept in mind that laboratory tests only indirectly estimate control of risk. In the end, only symptoms, exacerbations, and quality of life over time are the measures of asthma control."
American Thoracic Society guidelines on evaluation of chronic cough in gastro-esophageal reflux disease (GERD) (Irwin, 2006) stated that FENO measurements are not routinely recommended, because they do not appear to be helpful in diagnosing cough due to GERD.
Kowk et al (2009) examined the feasibility of obtaining FENO concentrations in 133 children aged 2 to 18 years, who were treated in the emergency department for acute asthma exacerbation and to examine the association between FENO concentrations and other measures of acute asthma severity. The investigators measured FENO concentrations before and 1 hour after the administration of corticosteroids and at discharge from the emergency department. Outcome measures included pulmonary index score (PIS), hospital admission, and short-term outcomes (e.g., missed days of school). The investigators reported that 68 % of the subjects provided adequate breaths for FENO measurement. The investigators found no difference in the median initial FENO concentration among subjects, regardless of the severity of their acute asthma. Most subjects showed no change in their FENO concentrations from the start to the end of treatment. The investigators stated that FENO concentrations were not significantly associated with other short-term outcomes. The investigators concluded that measurement of FENO is difficult for a large proportion of children with acute asthma exacerbation, and that FENO concentration during an asthma exacerbation does not correlate with other measures of acute severity and has limited utility in the emergency department management of acute asthma in children.
de Jongste et al (2009) found no added value of daily FENO monitoring with symptom monitoring versus symptom monitoring only. Children with atopic asthma (n = 151) were randomly assigned to 2 groups: (i) FENO monitoring plus symptom monitoring, or (ii) monitoring of symptoms only. All patients scored asthma symptoms in an electronic diary over 30 weeks; 77 received a portable NO analyzer. Data were transmitted daily to the coordinating centers. Patients were phoned every 3 weeks and their steroid dose was adapted according to FENO and symptoms, or according to symptoms. Children were seen at 3, 12, 21, and 30 weeks for examination and lung function testing. The primary end point was the proportion of symptom-free daysin the last 12 study weeks. The investigators reported that both groups showed an increase in symptom-free days, improvement of FEV1 and quality of life, and a reduction in steroid dose. None of the changes from baseline differed between groups.
A randomized clinical study of step-up therapy in children (n = 182) with uncontrolled asthma despite corticosteroids (Lemanske et al, 2010) found that patterns of differential response were not predicted by the fraction of FENO, either dichotomized at the median baseline value or examined as a continuous covariate. The authors stated that more expensive and labor-intensive measures of physiological factors (e.g., methacholine PC20) and biomarkers (e.g., the fraction of ENO) did not have predictive value.
Powell, et al. (2011) concluded that asthma exacerbations during pregnancy can be significantly reduced with a validated FENO-based treatment algorithm. The investigators reported on a double-blind, parallel-group, controlled trial in two antenatal clinics in Australia. The investigators randomly assigned 220 pregnant, non-smoking women with asthma to treatment adjustment at monthly visits by an algorithm using clinical symptoms (control group) or FENO concentrations (active intervention group). The primary outcome was total asthma exacerbations. The investigators reported that the exacerbation rate was lower in the FENO group than in the control group (0·288 versus 0·615 exacerbations per pregnancy; incidence rate ratio 0·496, 95% CI 0·325-0·755; p=0·001). In the FENO group, quality of life was improved (score on short form 12 mental summary was 56·9 [95% CI 50·2-59·3] in FENO group versus 54·2 [46·1-57·6] in control group; p=0·037) and neonatal hospitalizations were reduced (eight [8%] versus 18 [17%]; p=0·046). A limitation of this study is that the control group's algorithm differed from current guidelines and that significantly more women in the FENO group were receiving corticosteroids than in the control group.
Using a similar treatment algorithm, Pike, et al. (2012) concluded that FENO-guided inhaled corticosteroid titration did not reduce corticosteroid usage or exacerbation frequency in children with moderate to severe asthma. The investigators conducted a randomized controlled clinical trial to evaluate whether monitoring FENO can improve outpatient management of children aged 6 to 17 years with moderate to severe asthma. Ninety children were randomized to FENO-driven therapy or to a standard management group where therapy was driven by conventional markers of asthma control. Inhaled corticosteroids or long-acting bronchodilator therapies were altered according to FENO levels in combination with reported symptoms in the FENO group. Subjects were assessed twice monthly for 12 months. Inhaled corticosteroid dose and exacerbation frequency change were compared between groups in an intention to treat analysis. The investigators reported that no difference was found between the two groups in either change in corticosteroid dose or exacerbation frequency. The investigators stated that results were similar in a planned secondary analysis of atopic asthmatics.
Calhoun, et al. (2012) reported the results of the use of FENO in adults from the Best Adjustment Strategy for Asthma in the Long Term (BASALT) trial, a randomized controlled clinical trial conducted by the Asthma Clinical Research Network at 10 academic medical centers in the United States. The investigators found that, among adults with mild to moderate persistent asthma controlled with low-dose inhaled corticosteroid therapy, the use of either FENO-based or symptom-based adjustment of inhaled corticosteroids was not superior to physician assessment-based adjustment of inhaled corticosteroids in time to treatment failure. The investigators reported on the results of a randomized, parallel, 3-group, placebo-controlled, multiply-blinded trial of 342 adults with mild to moderate asthma controlled by low-dose inhaled corticosteroid therapy who were assigned to physician assessment-based adjustment, FENO-based adjustment, and symptom-based adjustment. For physician assessment-based adjustment and FENO-based adjustment, the dose of inhaled corticosteroids was adjusted every 6 weeks; for symptom-based adjustment, inhaled corticosteroids were taken with each albuterol rescue use. The primary outcome was time to treatment failure. The investigators reported that there were no significant differences in time to treatment failure. The 9-month Kaplan-Meier failure rates were 22% (97.5% CI, 14%-33%; 24 events) for physician assessment-based adjustment, 20% (97.5% CI, 13%-30%; 21 events) for FENO-based adjustment, and 15% (97.5% CI, 9%-25%; 16 events) for symptom-based adjustment. The hazard ratio for physician assessment-based adjustment versus FENO-based adjustment was 1.2 (97.5% CI, 0.6-2.3). The hazard ratio for physician assessment-based adjustment versus symptom-based adjustment was 1.6 (97.5% CI, 0.8-3.3).
An editorial accompanying the BASALT trial (O'Connor & Reibman, 2012) concluded that dose adjustment based on exhaled nitric oxide measurements has not been shown to improve outcomes in routine asthma management. The editorialist commented that the result of the BASALT trial is consistent with prior evidence that routine exhaled nitric oxide monitoring is not warranted for managing most patients with asthma. The editorialist noted that the recent American Thoracic Society practice guideline recommends the use of exhaled nitric oxide measurement “in monitoring airway inflammation in patients with asthma (strong recommendation, low quality of evidence),” but that, in light of the BASALT findings, it is difficult to justify additional health care expenditures for routinely monitoring exhaled nitric oxide in adults with mild to moderate asthma. The editorialist noted that there may be a role for exhaled nitric oxide measurement, however, when the diagnosis of asthma is not clear or for specific patient subgroups, but that further research is needed to identify the clinical scenarios in which exhaled nitric oxide measurement may improve clinical outcomes.
Lester, et al. (2012) reported on the use of a comprehensive asthma management program by an urban community health center. The program included serial FeNO measurements among several program components. Other components of the program were: use of asthma management guidelines; use of a team approach to asthma management; use of a standardized tool for screening for asthma risk factors, symptoms, and level of asthma control; use of a workflow algorithm and chart form incorporated into an electronic health record to collect data and track clinical measures for an asthma registry; use of asthma health educators to assist patients in setting asthma self management goals and educate them in asthma self-management; use of community resources (visiting nurses, a state-funded pest control program, and durable medical equipment vendors for products such as aerochambers and nebulizers); and regular followup, with frequency based upon asthma severity. The authors reported that 95.8 percent of patients enrolled in the program had an asthma severity assessment, 95.4 percent of persistent asthmatics were on anti-inflammatory medications, 68.2 percent of asthma patients have documented asthma self-management goals, and 5.2 percent of asthma patients have a self-reported visit to the emergency room in the six months preceding their most recent visit. Because the program includes multiple components, the contribution of FeNO measurements to these outcomes cannot be determined.
Guidelines from the British Thoracic Society and the Scottish Intercollegiate Guidelines Network (2008) stated that "more research needs to be done before recommendations can be made for the use of exhaled nitric oxide concentration." Updated guidelines from the Scottish Intercollegiate Guidelines Network (2009) stated that more experience with FENO and more information on the long-term response to corticosteroid in patients who do not have a raised FENO is needed before this approach can be recommended to identify patients who are going to respond to corticosteroid therapy.
Puckett and George (2008) stated that the airway NO flux and alveolar NO concentration can be elevated in adults and children with asthma and have been correlated with markers of airway inflammation and airflow obstruction in cross-sectional studies. They noted that longitudinal studies that specifically address the clinical potential of partitioning FENO for diagnosis, managing therapy, and predicting exacerbation are needed.
In a review on FENO in the diagnosis and management of asthma, Rodway and colleagues (2009) stated that further evidence of the clinical utility of FENO in asthma management is needed. The authors stated that,"[r]egardless of the rapid, convenient, and noninvasive nature of this test, additional well-designed, long-term longitudinal studies are necessary to fully evaluate the clinical utility of eNO in asthma management".
In a review on the utility of FENO in the diagnosis and management of asthma, Majid and Kao (2010) noted that "FeNO shows promise as a tool in the diagnosis and treatment of asthma. However, further studies are needed to address outstanding questions about its exact role in guiding asthma management".
Guidelines from the Global Initiative for Asthma (GINA, 2011) state that levels of FENO and carbon monoxide have been suggested as non-invasive markers of airway inflammation in asthma. The guidelines state that levels of FENO are elevated in people with asthma (who are not taking inhaled glucocorticosteroids) compared to people without asthma, yet these findings are not specific for asthma. The guidelines note the FENO has not been evaluated prospectively as an aid in asthma diagnosis, but these measurements are being evaluated for potential use in determining optimal treatment, "although it has been shown that the use of FeNO as a measure of asthma control does not improve control or enable reduction in dose of inhaled glucocorticosteroid." The Global Initiative for Asthma was launched in conjunction with the National Heart Lung and Blood Institute and the World Health Organization.
A Cochrane review evaluated clinical studies of the efficacy of tailoring asthma interventions based on FENO in comparison to clinical symptoms (with or without spirometry/peak flow) for asthma related outcomes in children and adults (Petsky et al, 2009). The assessment found that tailoring the dose of inhaled corticosteroids based on FENO in comparison to clinical symptoms was carried out in different ways in the 6 randomized controlled clinical studies that were included in the review, and the results showed only modest differences at best and potentially higher doses of inhaled corticosteroids in children. The authors of the Cochrane review concluded that the role of utilizing FENO to tailor the dose of inhaled corticosteroids is currently uncertain and can not be routinely recommended for clinical practice. In this Cochrane review, Petsky et al (2009) evaluated the effectiveness of tailoring asthma interventions based on FENO in comparison to clinical symptoms (with or without spirometry/peak flow) for asthma related outcomes in children and adults. These investigators searched the Cochrane Airways Group Specialised Register of Trials, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and reference lists of articles. The last search was completed in February 2009. All randomized controlled comparisons of adjustment of asthma therapy based on FENO compared to traditional methods (primarily clinical symptoms and spirometry/peak flow) were selected for analysis. Results of searches were reviewed against pre-determined criteria for inclusion. Relevant studies were independently selected in duplicate. Two authors independently assessed trial quality and extracted data. Two studies have been added for this update, which included 6 (2 adults and 4 children/adolescent) studies; these studies differed in a variety of ways including definition of asthma exacerbations, FENO cut-off levels, the way in which FENO was used to adjust therapy and duration of study. Of 1,053 randomized subjects, 1,010 completed the trials. In the meta-analysis, there was no significant difference between groups for the primary outcome of asthma exacerbations or for other outcomes (clinical symptoms, FENO level and spirometry). In post-hoc analysis, a significant reduction in mean final daily dose inhaled corticosteroid per adult was found in the group where treatment was based on FENO in comparison to clinical symptoms, (mean difference of -450 mcg; 95 % CI: -677 to -223 mcg budesonide equivalent per day). However, the total amount of inhaled corticosteroid used in one of the adult studies was 11 % greater in the FENO arm. In contrast, in the pediatric studies, there was a significant increase in inhaled corticosteroid dose in the FENO strategy arm (mean difference of 140 mcg; 95 % CI: 29 to 251 mcg budesonide equivalent/day). The authors concluded that tailoring the dose of inhaled corticosteroids based on FENO in comparison to clinical symptoms was carried out in different ways in the 6 studies and found only modest benefit at best and potentially higher doses of inhaled corticosteroids in children. The authors stated that the role of utilizing FENO to tailor the dose of inhaled corticosteroids can not be routinely recommended for clinical practice at this stage and remains uncertain.
An American Thoracic Society ad hoc committee was organized by the committee chairman to devise “interpretive strategies” for the different potential uses and applications of FENO (Dweik et al, 2011). The committee identified a number of potential uses of FENO, which were graded by the committee members on the strength of the recommendation and strength of the evidence. Several potential uses of FENO were identified, each of which were related to the use of FENO to identify steroid responsiveness. However, there is a lack of reliable evidence demonstrating that clinical outcomes are improved by using FENO to identify steroid responsiveness and direct patient care in persons with asthma. One of the recommendations, identification of eosinophilic airway inflammation, was judged by the Committee to be supported by “strong consensus” and “moderate quality evidence.” The report stated that the importance of identifying eosinophilic airway inflammation rests on its correlation with steroid responsiveness: “the finding that FENO correlates with eosinophilic inflammation suggests its use as indirect indicator not only of eosinophilic inflammation, but more importantly of the potential for steroid responsiveness.” However, the evidence cited to support the recommendation found widely varying correlations between FENO and other recognized measures of eosinophilic airway inflammation (biopsy, sputum , and bronchiolar lavage). Another potential use recommended by the Committee, the use of FENO to support the diagnosis of asthma in situations in which objective evidence is needed, was a “weak recommendation” based upon “moderate quality evidence.” The report explained that “the importance of FENO lies in its potential to identify steroid responsiveness, rather than the exact clinical diagnosis.” Other potential uses of FENO identified by the Committee were judged to have “low quality evidence”, including use of FENO to determine the likelihood of steroid responsiveness in individuals with chronic respiratory symptoms possibly due to airway inflammation, and use of FENO in monitoring airway inflammation in patients with asthma.
Jartti et al (2012) noted that FENO has gained interest as a non-invasive tool to measure airway inflammation in asthma since it reflects allergic inflammation. The authors stated that recent controlled clinical studies have, however, questioned its role in the management of asthma in children. To assess the clinical value of FENO in pediatric asthma management, the authors performed a meta-analysis on the controlled studies of childhood asthma management guided by repeated FENO measurements, and relevant publications on the confounders of FENO were reviewed. The authors concluded that the data suggested that utilizing FENO to tailor the dose of inhaled corticosteroids in children can not be recommended for routine clinical practice since there is a danger of excessive inhaled corticosteroid doses in children without meaningful changes in clinical outcomes. Many disease and non-disease related factors (most importantly atopy, height/age and infection) affect FENO levels that can easily confound the interpretation.
Petsky et al (2012) evaluated the efficacy of tailoring asthma interventions based on inflammatory markers (sputum analysis and FENO) in comparison with clinical symptoms (with or without spirometry/peak flow) for asthma-related outcomes in children and adults. Cochrane Airways Group Specialised Register of Trials, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and reference lists of articles were searched. The last searches were in February 2009. All randomized controlled comparisons of adjustment of asthma treatment based on sputum analysis or FENO compared with traditional methods (primarily clinical symptoms and spirometry/peak flow) were selected. Results of searches were reviewed against pre-determined criteria for inclusion. Relevant studies were selected, assessed and data extracted independently by at least 2 people. The trial authors were contacted for further information. Data were analysed as "intervention received" and sensitivity analyses performed. Six (2 adults and 4 children/adolescent) studies utilising FENO and 3 adult studies utilizing sputum eosinophils were included. These studies had a degree of clinical heterogeneity including definition of asthma exacerbations, duration of study and variations in cut-off levels for percentage of sputum eosinophils and FENO to alter management in each study. Adults who had treatment adjusted according to sputum eosinophils had a reduced number of exacerbations compared with the control group (52 versus 77 patients with greater than or equal to 1 exacerbation in the study period; p = 0.0006). There was no significant difference in exacerbations between groups for FENO compared with controls. The daily dose of inhaled corticosteroids at the end of the study was decreased in adults whose treatment was based on FENO in comparison with the control group (mean difference -450.03 μg, 95 % CI: -676.73 to -223.34; p < 0.0001). However, children who had treatment adjusted according to FENO had an increase in their mean daily dose of inhaled corticosteroids (mean difference 140.18 μg, 95 % CI: 28.94 to 251.42; p = 0.014). It was concluded that tailoring of asthma treatment based on sputum eosinophils is effective in decreasing asthma exacerbations. However, tailoring of asthma treatment based on FENO levels has not been shown to be effective in improving asthma outcomes in children and adults. The authors concluded that, at present, there is insufficient justification to advocate the routine use of either sputum analysis (due to technical expertise required) or FENO in everyday clinical practice.
Van Beek et al (2011) evaluated the potential usefulness of measuring FENO as a screening tool for pulmonary tuberculosis (TB). These researchers compared 90 consecutive smear-positive, culture-confirmed TB patients presenting at a referral hospital with office workers (no X-ray confirming TB) at a hospital (n = 52) and at a construction firm (n = 84). Exhaled NO levels were analysed using a validated hand-held analyser. Exhaled NO levels among TB patients (median 15 parts per billion [ppb], inter-quartile range [IQR] 10 to 20) were equal to those among construction firm workers (15 ppb, IQR 12-19, p = 0.517) but higher than those among hospital workers (8.5 ppb, IQR 5 to 12.5, p < 0.001). Taking the hospital workers as the comparison group, best performance as a diagnostic tool was at a cut-off of 10 ppb, with sensitivity 78 % (95 %CI: 68 to 86) and specificity 62 % (95 % CI: 47 to 75). Test characteristics could be optimized to 84 % versus 67 % by excluding individuals who had recently smoked or consumed alcohol. The authors concluded that while FENO measurement has limited value in the direct diagnosis of pulmonary TB, it may be worth developing and evaluating as a cost-effective replacement of chest X-ray in screening algorithms of pulmonary TB where X-ray is not available.
Phillips et al (2011) reviewed the data available on the sino-nasal application of nasal NO measurement, particularly its use as a diagnostic, prognostic, or treatment effect indicator. EMBASE 1980 to February 10, 2010; Medline 1950 to February 10, 2010; Cochrane Collaboration database; NHS Evidence Health Information Resources database were searched using a search strategy designed to include manuscripts relevant both to NO measurement and sinus or nasal problems. A title search was performed on these manuscripts to select those relevant to clinical or basic science aspects of NO measurement. A subsequent abstract search selected those manuscripts concerning the application of NO measurement to sino-nasal problems. The manuscripts selected were subject to a full-text review to extract data sets of nasal NO readings for different patient groups. Initially, 1,088 manuscripts were selected. A title search found 335 manuscripts of basic scientific or clinical interest. An abstract search found 35 manuscripts directly relating to NO measurement in sino-nasal disease. Full-text analysis produced 20 studies with extractable data on nasal NO levels in clearly defined patient groups. Studies did not show sufficient homogeneity to enable substantial meta-analysis of aggregated data. The authors stated that the literature concerning nasal NO is marked by many theories concerning its role in the nose. However, clinical studies show a wide range of measurement methods, the presence of various confounding factors, and heterogeneity of study populations. Although both the presence of nasal polyps and opening of the sinuses surgically seem to have an effect on nasal NO levels, there is no evidence in any population that low nasal NO causes harmful effects. They concluded that current evidence shows that nasal NO is not a clinically useful measure for sino-nasal disease.
Yoon and Sin (2011) stated that chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality in the world. None of the current treatments, except for smoking cessation and supplemental domiciliary oxygen for hypoxemic patients, can modify its natural course or alter survival. The pipeline for new compounds is not very promising owing to repeated failures, and many large pharmaceutical companies have abandoned COPD drug discovery altogether. One major barrier to new drug discovery is the lack of modifiable biomarkers that can be used as surrogates of clinical outcomes such as exacerbation and mortality. The only accepted marker in COPD is FEV1. However, by definition, COPD is a non-reversible or poorly reversible condition with respect to FEV1. Thus, very few drugs except for bronchodilators have been able to address this endpoint. Of many candidate molecules, sputum neutrophil counts, FENO and proline-glycine-proline (PGP) and N-α-PGP, which are breakdown products of collagen, are promising lung-based biomarkers. However, their clinical utility has not been validated in large clinical trials. Promising blood biomarkers include surfactant protein D, and pulmonary- and activation-regulated chemokine (PARC/CCL-18). However, the clinical data have been inconsistent. Non-specific inflammatory biomarkers such as C-reactive protein and interleukin-6 lack specificity for COPD and thus are of limited clinical usefulness.
Furthermore, in a review on "Biomarkers in chronic obstructive pulmonary disease", Rosenberg and Kalhan (2012) concluded that "So far, no single biomarker in COPD warrants wide acceptance emphasizing the need for future investigation of biomarkers in large-scale longitudinal studies".
Exhaled Breath Condensate pH
Exhaled breath condensate (EBC) is a non-invasive method for studying the composition of the fluid lining the airway. Researchers have reported abnormalities in EBC concentrations of at least 12 markers in individuals with inflammatory lung disorders. The measurement of EBC pH is one EBC marker that is currently being investigated as a method for assessing asthma and other chronic pulmonary diseases.
Investigators have found that EBC pH values of individuals with respiratory disease (e.g., asthma and other chronic pulmonary diseases) are lower compared with those of healthy controls and that pH levels increase towards control levels after steroid treatment (Kharitonov, 2004; Carpagnano et al, 2004, 2005; Carraro et al, 2005; Effros et al, 2005).
In a study presented at the 2004 Annual Meeting of the American Academy of Allergy, Asthma and Immunology (AAAAI), researchers reported that the pH of EBC in acute asthmatic children was significantly lower than those with stable asthma. Brunetti and colleagues tested 104 asthmatic children with skin prick tests, lung function tests, and EBC pH measurements. The children experiencing asthma exacerbations received steroid and beta-2 agonist treatment for one week before the pH test was repeated. Thirty-four children (34.7 %) showed evidences of acute asthma and 70 children (67.3 %) had stable asthma. After treatment, the EBC pH of patients with acute asthma was significantly higher than before therapy.
Several researchers, however, have raised concerns regarding the standardization of EBC collection and measurement methods. A recent consensus panel convened by the American Thoracic Society/European Respiratory Society Task Force on EBC (Horvath, 2005) provided general recommendations for both EBC collection and measurement. However, the Task Force stated that more studies are necessary before EBC can be recommended for clinical practice. The following areas for future research were identified: (i) mechanisms and site of EBC particle formation; (ii) determination of dilution markers; (iii) improvement of reproducibility; (iv) longitudinal studies are needed; and (v) determination of the utility of EBC measures in the management of individual patients.
In a review of EBC in chronic obstructive pulmonary disease, Effros et al (2005) stated that EBC pH measurements may not provide accurate estimates of airway pH. Data interpretation is complicated by uncertainty regarding the source of condensate solutes and by variable dilution of respiratory droplets from condensed water vapor, which represents more than 99.9 % of condensate volumes. Furthermore, the Guidelines from the Global Initiative for Asthma (GINA) (2004) stated that neither sputum eosinophilia nor exhaled gases have been evaluated prospectively as an aid in the diagnosis of asthma. The guidelines state that there is a need to develop further noninvasive discriminate measurements of airway inflammation.
Exhaled breath condensate pH is a novel, noninvasive research approach to monitor lung diseases; however, well-designed controlled studies are needed to establish the clinical utility of EBC pH for the assessment of asthma and other chronic pulmonary diseases.
Baraldi and Carraro (2006) stated that EBC is still only a research tool. Ko et al (2007) stated that there is some evidence that certain markers in EBC differ between patients with asthma and controls, and some markers may correlate with asthma severity and lung function, but there are many methodologic pitfalls with EBC assessment that limit its clinical applicability at present. The authors concluded that more studies are needed before this technique can be recommended for clinical use.
Cepelak and Dodig (2007) stated that in spite of many scientific studies involving lung disease patients, methodology for EBC collection and analysis has not yet been realized for daily utilization. Additional studies of the exact origin of condensate constituents and standardization of the overall analytical process, including collection, storage, analysis and result interpretation, are needed. Irrespective of these limitations, further investigation of this sample type is fully justified by the fact that classical specimens used in the management of pulmonary diseases are either obtained by invasive procedures (e.g., induced sputum, biopsy, broncho-alveolar lavage) or can not provide appropriate information (e.g., urine, serum). Analysis of EBC in the future might contribute significantly to the understanding of the physiological and pathophysiological processes in lungs, to early detection, diagnosis and follow-up of disease progression, and to evaluation of therapeutic response.
Guidelines from the National Asthma Education Program (NIH, 2007) stated that many biomarkers have been proposed, including concentration of hydrogen ions and various other metabolites in an exhaled breath condensate, but that few studies have validated these markers. The guidelines stated that these biomarkers may have a role in asthma management in the future.
Chan and colleagues (2009) stated that breath analysis, which includes gaseous phase analysis that measures volatile organic compounds using electronic noses, FENO, and EBC, has been proposed as a non-invasive and simple technique to investigate neoplastic processes in the airways. Exhaled breath condensate can be easily collected by breathing into a cooling system that condenses the water vapor in the breath. It has already been suggested to be a useful method to monitor severity of diseases such as asthma and to act as a surrogate measure of compliance to medical therapy. Presently, there still remains a relative paucity of lung cancer research involving EBC. However, since EBC is a simple, non-invasive technique that can be easily performed, even in ill patients, it has the potential to be validated for use in screening for the early diagnosis of lung cancer.
Dalaveris and associates (2009) evaluated the levels of vascular endothelial growth factor (VEGF), 8-isoprostane and tumor necrosis factor (TNF)-alpha in EBC and serum of patients with primary lung cancer prior to the initiation of any treatment, in order to evaluate their possible diagnostic role. Furthermore, associations between VEGF, 8-isoprostane and TNF-alpha levels in EBC and serum with clinicopathologic factors were examined. These researchers enrolled 30 patients with lung cancer (mean age of 65.2 +/- 10.5 years) and 15 age- and gender-matched healthy smokers as controls. Serum and EBC were collected before any treatment; TNF-alpha, VEGF and 8-isoprostane levels in EBC and serum were analyzed by an immunoenzymatic method. A statistically significant difference was observed between lung cancer patients and the control group regarding the values of TNF-alpha, both in EBC (52.9 +/- 5.0 pg/ml versus 19.4 +/- 3.9 pg/ml, p < 0.0001) and serum (44.5 +/- 6.3 pg/ml versus 22.2 +/- 4.3 pg/ml, p = 0.035). Moreover, EBC VEGF levels were higher in patients with T3-T4 tumor stage compared to T1-T2 (9.3 +/- 2.8 pg/ml versus 2.3 +/- 0.7pg/ml, p = 0.047). A statistically significant correlation was also observed between serum and EBC values of VEGF (r = 0.52, p = 0.019). In addition, serum levels of VEGF were higher in lung cancer patients than in controls (369.3 +/- 55.1 pg/ml versus 180.5 +/- 14.7 pg/ml, p = 0.046). Serum VEGF levels were also higher in patients with advanced stage of disease (IIIB-IV) and distant nodal metastasis (N2-N3). No differences were observed in 8-isoprostane in EBC between lung cancer patients and controls. In contrast, serum 8-isoprostane levels were higher in lung cancer patients compared to controls (24.9 +/- 3.6 pg/ml versus 12.9 +/- 1.6 pg/ml, p = 0.027) and were higher in patients with advanced disease. All 3 biomarkers presented acceptable reproducibility in the EBC on 2 consecutive days. The authors concluded that TNF-alpha, VEGF and 8-isoprostane are elevated in the serum of lung cancer patients and increased serum VEGF and 8-isoprostane levels are related to advanced disease. In EBC, increased TNF-alpha levels were observed in lung cancer patients, whereas increased VEGF levels were observed in advanced T-stage. They stated that further longitudinal studies are needed for the evaluation of the prognostic role of these biomarkers in lung cancer.
Fila and Musil (2010) stated that examination of EBC belongs to experimental methods that are used in many pulmonary diseases and it can take part in the study of their pathophysiology. Many biomarkers of inflammation and oxidative stress were studied in EBC in cystic fibrosis. Examination of pH of EBC is considered to be useful in evaluation of inflammatory acidification of airways, together with evaluation of response to antibiotic treatment of pulmonary exacerbation, due to immediately accessible result. Other important biomarkers include 8-isoprostane and 3-nitrotyrosine as markers of oxidative stress (both with negative correlation with pulmonary function) and leukotriene B4 as marker of neutrophilic inflammation. Opposite to other pulmonary diseases, hydrogen peroxide does not belong to useful markers of oxidative stress in cystic fibrosis, due to abundant reduced thiols and glutathione peroxidase in sputum of these patients. Attempts to detect bacterial DNA in EBC in cystic fibrosis also failed. In spite of mentioned progress, examination of EBC remains a research method and it has not been introduced into clinical practice.
Teng et al (2011) examined if EBC hydrogen peroxide (H(2)O(2)) is elevated in people with asthma and if it reflects disease severity and disease control or responds to corticosteroid treatment. Studies were identified by searching PubMed, Embase, Cochrane Database, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and www.controlled-trials.comfor relevant reports published before September 2010. Observational studies comparing levels of EBC H(2)O(2) between patients with asthma who were non-smokers and healthy subjects were included. Data were independently extracted by 2 investigators and analyzed using Stata 10.0 software. A total of 8 studies (involving 728 participants) were included. EBC H(2)O(2) concentrations were significantly higher in patients with asthma who were non-smokers compared with healthy subjects, and higher values of EBC H(2)O(2) were observed at each level of asthma, classified either by severity or control level, and the values were negatively correlated with FEV1. In addition, EBC H(2)O(2) concentrations were lower in patients with asthma treated with corticosteroids than in patients with asthma not treated with corticosteroids. The authors concluded that H(2)O(2) might be a promising biomarker for guiding asthma treatment; however, further investigation is needed to establish its role.