FeNO
FeNO or fraction of exhaled nitric oxide, has emerged
in recent years as one of the new tests to diagnose and monitor asthma. Asthma
is one of the most common diseases in humans, with children especially
afflicted. The diagnosis of asthma is primarily a clinical one and the management
too has been based more on the clinical sense of the treating physician.
However, with increasing patient populations and more information about new
subtypes of asthma, a test was needed to help support the clinician’s diagnosis
and management strategy. FeNO has stepped up to meet the gap.
It may come as a surprise to many that the normal lungs
produce some amounts of nitric oxide or NO. The amount produced is minuscule
though, in parts per billion. In disease states - such as asthma – the amount
of NO produced increases significantly. This finding cal be exploited in
routine clinical practice to support the diagnosis of asthma and to monitor
treatment.
Asthma is mainly of two types – eosinophil predominant and
non-eosinophil predominant (eosinophils are a kind of blood cell). The
eosinophil predominant type of asthma responds very well to inhaled steroids
while the non-eosinophil type does not. Therefore, the differentiation of
asthma into these two subtypes is of importance in the management of the
disease. The only way to do this other than the use of FeNO is to do sputum
(saliva) analysis, which besides being messy is also time consuming. The FeNO
test can be very helpful in this situation. FeNo levels will be high in
patients with eosinophil predominant asthma and will be normal in the
non-eosinophil predominant subtype. So, by checking the FeNO levels one can
decide whether or not to start inhaled steroids.
FeNO levels are very useful in monitoring the response to
treatment. In patients who are compliant with treatment and are improving, the
FeNo levels should fall. In patients in whom there is a partial improvement,
checking serial FeNO levels will help in decision making, i.e. whether to stop,
decrease or increase treatment. These levels can used in conjunction with
standard spirometry for additional information.
Children are often unable to perform rigorous pulmonary
function testing. They find it easier to perform FeNO testing, which is done by
gently blowing into the mouthpiece of the measuring device for 10 – 12 seconds.
The result is subsequently displayed on the screen in a few seconds.
In summary, FeNo is a non-invasive, easy to perform, quick
and reliable test which is an useful adjunct in the management of asthma,
especially in children and difficult cases.
