Exhaled Nitric Oxide (ENO) Test

Exhaled Nitric Oxide

A lot can be cleaned from the air we exhale. When something goes wrong within our bodies, the things we expel or exhale can be studied to figure out what is going on.

What is an Exhaled Nitric Oxide (ENO) test?

Nitric oxide is produced by the body when there is inflammation or swelling in the respiratory tract. High levels of nitric oxide in exhaled air can help diagnose the following respiratory conditions:

  • Asthma: chronic medical condition that results in the inflammation and swelling of the lower respiratory tract in your lungs.
  • Allergies: increased nitric oxide levels have been observed in individuals with allergic rhinitis.

An exhaled nitric oxide test measures the amount of nitric oxide present in your breath each time you exhale. High nitric oxide levels might indicate inflamed or swollen airways caused by certain respiratory conditions such as asthma and allergic rhinitis. 

How does an ENO test work?

An exhaled nitric oxide test is non-invasive and is similar to a spirometry in Singapore, which is a type of lung function test. It is usually performed in an outpatient setting and takes less than 5 minutes. 

You must wear loose and comfortable clothing. Loosen your jewelry as they might restrict your breathing or cause problems with the test. An exhaled nitric oxide test is carried out in the following way:

  • A soft clip will be placed over your nose. This ensures that all your breathing (inhaling and exhaling) goes through your mouth and not your nose.
  • A tube-like device with a sterile mouthpiece attached, is placed into your mouth and you are to inhale and exhale into it. 
  • Exhale slowly and steadily until you hear a beep.
  • As you are exhaling, your results are being interpreted by a computer.
  • You must repeat the tests several times to ensure that the results are accurate.

What happens after an Exhaled Nitric Oxide test?

Lung function tests are non-invasive, this means you will be able to return to your normal activities immediately. Once your respiratory specialist has anaylsed your results, he/she will discuss them with you and decide what the next steps are.

High levels of nitric oxide are often an indication of inflammation in the respiratory tract and asthma. Your test results could indicate the following:

  • If steroids such as corticosteroids will be useful in the treatment or management of your asthma.
  • If your current medication is effective in managing your asthma.
  • If your treatment plan must be modified for better management.

Who needs an Exhaled Nitric Oxide test?

An exhaled nitric oxide test is usually used in individuals for the following reasons:

  • Diagnose asthma
  • Diagnose allergies
  • Find out if medication has improved asthma

How do I prepare for an Exhaled Nitric Oxide test in Singapore?

An exhaled nitric oxide test has little preparation besides avoiding the following at least an hour before the test:

  • Caffeine 
  • Alcohol
  • Smoking
  • Foods rich in nitrates such as green leafy vegetables

These might affect test results, making them less accurate.

What are the benefits of an Exhaled Nitric Oxide test?

  • Non-invasive
  • No downtime
  • Fast diagnostic test
  • Improves management and treatment of asthma

What are the common risks or complications of an Exhaled Nitric Oxide test in Singapore?

An exhaled nitric oxide test is a relatively safe procedure with a very low risk of side effects. A small amount of people might feel lightheaded from the repeated breathing in and out, but this feeling will go away after a short rest.

Frequently asked questions

What are the normal levels of nitric oxide?

Normal levels are <25 of parts per billion (ppb), slightly elevated levels are 25-50 ppb, and highly elevated levels are >50 ppm.

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