Study selection criteria
| Inclusion | Exclusion | |
| Population | Adults (≥18 years) with diagnosis of asthma including pregnant women. | Studies that included cohorts with a mean age <18 years of age Recruited patients were not diagnosed with asthma Animal models Unselected specific population (e.g. firefighters, obese or athletes) |
| Intervention | Studies that measured FeNO according to the ATS 2005 criteria [20] for the management of asthma, either with or without other indicators of asthma control. ATS criteria relating to multiple testing were relaxed to allow inclusion of studies that operated electrochemical devices in line with the manufacturer's instructions, which state only one test is required. Studies where monitoring was performed at home were excluded as this was not within the scope of the assessment. | Device which is not validated for measuring FeNO Offline measurements Studies where FeNO is measured on a more regular basis (i.e. not during a routine annual review) |
| Comparator | Studies comparing the intervention to any other management strategy that does not utilise FeNO measurements. | Includes the use of FeNO measurement as part of the management strategy |
| Outcome | Primary outcome of interest included incidence of acute exacerbation (any definition of exacerbation severity was acceptable, including “use of oral corticosteroids”), inhaled corticosteroid use, unscheduled contact with healthcare officials, hospitalisations and emergency department visits expressed or calculable as rates per person year or as the number of patients experiencing exacerbations. These outcomes were chosen as they have the greatest impact both clinically and economically. Other outcomes included clinical complications associated with acute exacerbation, asthma control and symptoms, adverse events, health-related quality of life, mortality and compliance. | Does not report data on FeNO-guided step-up/step-down therapy Measure of alveolar nitric oxide or nasal nitric oxide |
| Study type | Randomised controlled trials. | Preclinical and biological studies Editorials and opinion pieces Studies only published in languages other than English |
FeNO: fractional exhaled nitric oxide; ATS: American Thoracic Society.