Nitric Oxide Test for Asthma

1 What is a Nitric Oxide Test for Asthma?

The exhaled Nitric Oxide (eNO) test is used for the diagnosis of respiratory diseases like asthma. It measures the level of nitric oxide gas in the exhaled breath of the patient.

Nitric Oxide (NO) is found in the exhaled breath of all humans. But patients with asthma tend to have high levels of NO in their exhaled breath. The patient is asked to blow air into a breath-analyzer, in order to collect the sample.

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2 Reasons for Procedure

Here are the most common reasons to undergo a nitric oxide test for asthma. Asthma is usually diagnosed by analyzing the medical history of the patient followed by a physical exam and certain tests such as peak flow measurement and spirometry tests which are performed for knowing the status lungs.

Sometimes the doctor may recommend tests known as challenge tests, which trigger  asthma symptoms and then treat mild asthma. Although, at times the diagnosis may remain uncertain with these tests.

Thus in these cases, the exhaled nitric oxide test may be helpful. Nitric oxide is produced by almost all the organs of the body, including the lungs. It helps in fighting inflammation and relaxing the constricted muscles.

High levels of exhaled nitric oxide are considered to be a sign of asthma. Nitric oxide testing is also done to predict whether steroid medications (which decrease inflammation) are likely to be helpful for your asthma or not. It may also be used by the doctor as a confirmatory test for asthma.

3 Potential Risks

There are no potential risks associated with the nitric oxide test for asthma.

4 Preparing for your Procedure

Following steps should be followed in preparing for nitric oxide test for asthma:

  • Maintain a copy of all previous consultations and tests you've had regarding this problem.
  • Ask if there's anything which has to be done or not to be done, such as restricting your diet.
  • Make a list of all the related and even unrelated symptoms.
  • Prepare a list of all the medications.

The doctor will suggest the patient to go for exhaled Nitric Oxide (eNO) test if asthma is suspected.

He/she will ask the patient to avoid the following things for at least two hours before the test for accurate results:

  • Using an asthma inhaler
  • Eating and drinking
  • Exercising
  • Use of tobacco, toothpaste or mouthwash

5 What to Expect

Read on to learn more about what to expect during and after your nitric oxide test for asthma.

During the test procedure, the doctor may put a mouthpiece into the patient’s mouth, which is attached to a tube that leads to an electronic measurement device.

The patient is then asked to breathe in for two or three seconds until his/her lungs are filled with air. This is followed by a steady exhale so that the air flows out of the lungs at a steady rate.

The breathing rate can be observed on the monitor. The test is often repeated a few times to confirm the results. The entire test generally takes five minutes or less.

6 Procedure Results

Results of nitric oxide test for asthma vary from person to person thus doctor has to consider following points for making accurate diagnosis:

  • Patients signs and symptoms
  • Peak flow test or spirometry test results
  • Previous nitric oxide tests results
  • Medications you take
  • Whether the patient is suffering from flu or cold
  • Whether the patient has hay fever or other allergies
  • Whether the patient smokes or not
  • Age of the patient

Normal nitric oxide levels are considered to be less than 20 parts per billion for children and less than 25 parts per billion for adults.

Nitric oxide levels higher than 35 parts per billion in children whereas, 50 parts per billion in adults are considered signal of airway inflammation caused by asthma.

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