Spirometry – Normal Values and Test Results

What is spirometry?

To take a spirometry test, you sit and breathe into a small machine called a spirometer. This medical device measures the amount of air you inspire or expire and the speed of your breath.

Spirometry is a standard pulmonary function test doctors use to measure how well your lungs are functioning. The test works by measuring the amount of air inspired and expired through your lungs.

Spirometry tests are performed to diagnose these conditions:

  • COPD
  • emphysema
  • asthma
  • bronchitis
  • restrictive lung disease (such as interstitial pulmonary fibrosis)
  • other disorders affecting lung function

They also allow your doctor to examine chronic lung conditions to check that your current treatment is upgrading your breathing.

Spirometry is usually performed as part of a group of tests called pulmonary function tests.

How to prepare for a spirometry test

You shouldn’t smoke one hour before a spirometry test. You’ll also require to avoid alcohol that day as well. Eating too large amount of a meal could also affect your ability to breathe.

Don’t wear very tight clothing that it could restrict your breathing. Your doctor may also have instructions about whether you should avoid using inhaled breathing medications or other medications previous to your test.

Spirometry procedure

A spirometry test often takes about 15 minutes and usually performed in your doctor’s office. Here’s given how spirometry test is performed:

  1. You’ll be seated in a chair in an examination room at your doctor’s clinic. Your doctor or a nurse closes your nostrils with the help of a clip.They also place a cup-like breathing mask around your mouth.
  2. Your doctor or nurse then tells you to take a deep breath in, hold your breath for a few seconds, and then exhale with lots of force into the breathing mask.
  3. You’ll repeat this test at least three times to make sure that your results are stable. Your doctor or nurse may have you repeat the test many times if there is a lot of difference between your test results. They’ll take the highest value from three close test readings and use it as your final result.

If you have proof of a breathing disorder, your doctor might then give you an inhaled medication called bronchodilator to open up your lungs after the first round of tests. He will then ask you to wait for 15 minutes before doing another round of test. Subsequently, your doctor will compare the results of the two measurements to see whether the bronchodilator helped increase your airflow.

When used to monitor breathing disorders, a spirometry test is generally performed once a year to once every two years to examine changes in breathing in people with well-controlled COPD or asthma. Those with more severe breathing issues or breathing problems that aren’t well managed are suggested to have repeated spirometry tests.

Spirometry side effects

Few complications can occur during or after a spirometry test. You may feel little dizziness or have some shortness of breath (dyspnea) right away after performing the test. In very rare cases, the test may stimulate severe breathing problems.

The test needs some exertion, so it is not suggested if you recently had a heart condition or have other heart complications.

Spirometry normal values and how to read your test results

Normal results for a spirometry test differ from person to person. These tests depend on your age, height, race, and gender. Your doctor calculates the predicted normal value for you before you do the test. Once you’ve completed the test, they examine your test score and compare that value to the predicted value. Your result is regarded as normal if your score is 80 percent or more of the predicted value.

You can get a normal idea of your predicted normal value with a spirometry calculator. The Centers for Disease Control and Prevention provides a calculator that lets you enter your particular details. If you know your spirometry results previously, you can enter those as well, and the calculator will tell you what percent of the predicted values your results are.

Spirometry measures two main factors: expiratory forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). Your doctor also examines these as a combined number called the FEV1/FVC ratio. If you have blocked airways, the amount of air you’re able to quickly exhale out of your lungs will be lowered. This interprets to a lower FEV1 and FEV1/FVC ratio.

FVC measurement

One of the basic spirometry measurements is FVC, which is the highest total amount of air you can forcefully expire after breathing in as deeply as you can. If your FVC is lower than normal, something is restricting or limiting your breathing.

Normal or abnormal results are assessed differently between adults and children:

For children ages 5 to 18:

If Percentage of predicted FVC value is 80% or more then result is normal and if less than 80% then result is abnormal

For adults: FVC Result is higher than or equal to the lower limit of normal then result is normal, if less than lower limit of normal then result is abnormal.

An abnormal FVC could be because of restrictive or obstructive lung disease, and other types of spirometry measurements are needed to find out which type of lung disease is present. An obstructive or restrictive lung disease could be present by itself, but it’s possible to have both of these two types at the same time.

FEV1 measurement

The second main spirometry measurement is forced expiratory volume (FEV1). This is the amount of air you can force out of your lungs in one second. It can help your doctor to assess the severity of your breathing complications. A lower-than-normal FEV1 reading shows you might have a remarkable breathing obstruction or blockage.

Your doctor will use your FEV1 measurement to grade the severity of any abnormalities. The following chart outlines what’s regarded as normal and abnormal when it comes to your FEV1 spirometry test results, according to guidelines from the American Thoracic Society:

Percentage of predicted FEV1 value

80% or more – normal

70%–79% – mildly abnormal

60%–69% – moderately abnormal

50%–59% – moderate to severely abnormal

35%–49% – severely abnormal

Less than 35% – very severely abnormal

FEV1/FVC ratio

Doctors usually examine the FVC and FEV1 separately, and then calculate your FEV1/FVC ratio. The FEV1/FVC ratio is a number that constitutes the percentage of your lung capacity you’re able to exhale in one second. The higher the percentage derived from your FEV1/FVC ratio, in the absence of restrictive lung disease that causes a normal or increased FEV1/FVC ratio, the healthier your lungs are. A low ratio recommends that something is blocking or obstructing your airways:

5 to 18 years of age :

low FEV1/FVC ratio – less than 85%

adults :

low FEV1/FVC ratio – less than 70%

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