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FeNO Testing

FeNO stands for fractional exhaled nitric oxide. This is a gas found in the atmosphere, and your body produces it when there is inflammation in your airways. 

FeNO testing has been used since the 1990s to measure the amount of nitric oxide in your airways. A high level of nitric oxide is a sign of inflammation and is common in people with asthma, allergies, and eczema. 

A FeNO test can diagnose asthma but can’t be used as the only diagnostic tool. It can help to confirm an asthma diagnosis and to rule out similar conditions.

What a FeNO Test Measures

A FeNO test measures the amount of fractional exhaled nitric oxide in your airways. It measures how much nitric oxide is present when you breathe out. If you have a high amount of nitric oxide in your breath, you have inflammation of your airways. 

Nitric oxide is measured in parts per billion (ppb).

For adults, a low nitric oxide level is defined as under 25ppb. An intermediate level, where asthma is likely, is between 25-50ppb. A reading over 50ppb means that asthma is highly likely. 

The numbers are different for children. A low nitric oxide level, where asthma is unlikely, is under 20ppb. An intermediate level of nitric oxide is between 20-35ppb. A high level of nitric oxide is anything over 35ppb. 

One’s nitric oxide level is a good indicator of whether you have asthma. This test can also help to establish a baseline, so we can see if your nitric oxide levels decline or increase.

How it Can Help Those with Asthma

A FeNO test can be helpful in several ways. We use it to rule out an asthma diagnosis. 

However, once you do have an asthma diagnosis, FeNO testing can be used to establish a baseline and determine if your treatment is effective. Most health insurances cover the cost of FeNO testing.

How a FeNo Test Works for Asthma

Preparing for a FeNO test is really simple. There are just a few things you need to avoid an hour before you take the test.

  • Don’t eat any foods that are rich in nitrates.
  • Do not consume any caffeine or alcohol. 
  • Do not use your steroid or rescue inhaler. 

If you do any of the above things, let us know, and we can reschedule this test. 

With a FeNO test, you breathe slowly into a tube while the machine measures your nitric oxide levels. 

For the test, you will complete the following steps: 

  1. Put clips on your nose.
  2. Breathe out.
  3. Put the device's mouthpiece in your mouth and breathe in slowly. 
  4. Slowly breathe out until the device starts to beep. 
  5. Continue breathing in and out as instructed. 

This test may make you a little lightheaded for a while, but that will quickly pass. After the test, stay seated and allow your breathing to return to normal. If you don’t feel well, let us know.

Accuracy of a FeNO Test

FeNO testing can provide a fairly accurate reading of nitric oxide levels in your airways.

However, the reading may not be accurate if you have been treated with inhaled steroids. Certain beverages and foods rich in nitrates can also impact test results. This includes:

  • Alcohol
  • Caffeine
  • Beetroot
  • Green leafy vegetables
  • Pork products

Don’t consume these an hour before your test to get the most accurate results. 

FeNO is best used to support an asthma diagnosis. Also, FeNO levels don’t always increase when your airway is inflamed. 

When You Should Have a FeNO Test

There are a few times when you should take a FeNO test. It can help diagnose asthma, check to see how well your asthma treatment is working, and it can be part of a routine check-up after an asthma diagnosis. 

A FeNO test can be repeated every 2 to 3 months to measure the level of inflammation in your airways. 

Advantages of a FeNO Test

There are some advantages of taking a FENO test. A few benefits of FeNO testing include: 

  • It is quick and only takes a few minutes.
  • It is a noninvasive test.
  • The test has little or no side effects.
  • The preparation for the test is simple.
  • You get immediate results from the test.

A few drawbacks of a FeNO test include:

  • It has to be completed in a doctor’s office.
  • It cannot diagnose all types of asthma.
  • It can’t be used for children under five years old to diagnose asthma.
  • It can cause very short-term lightheadedness.

However, the advantages of a FeNO test outweigh the drawbacks, as it is quick, easy, and provides immediate information. 

FeNO Testing in Portland, Oregon

At West Hills Allergy & Asthma Associates, Dr. Anderson-Cowell has more than two decades of experience diagnosing and treating patients with asthma. 

One tool for diagnosing asthma is FeNO testing. If you think you have asthma, reach out to us.

If you’re looking for expert diagnostic experience and effective treatment history, Dr. Anderson-Cowell can help. For a consultation, please call (503) 297-4779 or request an appointment online.

9701 SW Barnes Road
Suite 130
Portland, Oregon 97225


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