ABSTRACT
Measurement of fractional concentration of exhaled nitric oxide (FENO) is not strictly a test of respiratory function as it does not relate to the structure, mechanics, or physiology of the respiratory system. Measurement of FENO should be made prior to any other pulmonary function tests which require a forced manoeuvre. Such forced manoeuvres may increase the release of nitric oxide (NO) synthase from the respiratory epithelium, giving a false positive result on subsequent testing. Patients with asthma cluster into several subtypes, based upon demography, clinical features, and markers of airway inflammation. Although these subtypes are often referred to as phenotypes, there is no strong relationship to specific pathological features. Measurement of FENO is a relatively new test in respiratory medicine, which has recently made the transition from the research lab to clinical practice. Although its use is strongly supported by some expert opinion, there is as yet little evidence to show better outcomes when management is guided by this tool.
