Nice | Exhaled nitric oxide measurement in asthma

This new guideline from NICE looks at measuring exhaled Nitric Oxide (eNO) in asthma. I have never heard of this, so I'll just lay out the guidance and then give a bit more of an explanation as to what this is all about.

NICE recommendations

Measuring eNO is recommended as an option to aid diagnosis of asthma in both adults and children if:

  • There is an intermediate possibility of them having asthma (helpfully defined as where the diagnosis is uncertain)
  • It is done in combination with other diagnostic options (eg clinical judgment / spirometry / reversibility testing etc).

It is recommended as an option to support management in people who are symptomatic despite using inhaled steroids.

So want to know more?

What is the technology?

Nitric Oxide is released during an inflammatory response and its levels rise in people with asthma, or during exacerbations of asthma. Hand-held devices can measure eNO levels. The patient breaths out into them (like for spirometry) and the eNO is then measured. Wikipedia explains more.

Is the test any good?

This is quite a difficult question to answer. The problem is that there is no gold-standard for diagnosing asthma, so there is nothing brilliant to compare it to. However it does seem to be useful. It is more useful as a 'rule-in' test than as a 'rule-out' test. A positive result makes asthma likely, but a negative result, doesn't rule asthma out.

This is why NICE advises its use only if there is an uncertain diagnosis. If asthma is either clinically likely or unlikely, then the eNO is less likely to be helpful.

Is it useful during exacerbations?

At the moment, they are not advising its use to diagnose or assess severity of exacerbations, but as eNO levels do rise during exacerbations, it is possible that this use may come in the future.

Is it helpful during regular reviews?

Probably. NICE are obviously suggesting that it can be used 'as an option' in assessing people who are still symptomatic despite inhaled steroid use. This is firstly as, if it is negative, this may suggest that further investigations are needed to see if the patient definitely does have asthma. Secondly, it may be a marker of compliance, so it may suggest that people are not using their steroids as they should be.

Louise Hudman

I'm a freelance GP locum in Winchester & Southampton.

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