How Spirometry Is Used in Asthma

Man using a spirometer
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If you have been diagnosed with asthma, you will probably ask to undergo a procedure called spirometry. Spirometry is a common test which measures both how much and how fast air moves through your lungs. It is much more reliable test than the peak expiration flow (PEF), which only measures the speed of expiration.

While spirometry cannot diagnose asthma on its own, it is one of the tools used to make a diagnosis.

It also aids the management of your disease and can be used to monitor its progression over time. The spirometry test is performed in a doctor's office and can take anywhere from 10 to 30 minutes, depending on the evaluation.

How a Spirometer Is Used

Spirometry allows your doctor to measure several aspects of your lung function to determine both the severity of your asthma and the control of your symptoms. The three key measurements are:

A spirometer consists of a mouthpiece connected to a hand-held device that measures results as you breathe. When being tested, you will be given a nose clip to prevent you breathing through the nostrils. After inhaling deeply, you will be asked to exhale forcefully and for as long as possible.

Spirometry will usually be repeated three times to record your best result. You may also be asked to repeat the test after using a short-acting bronchodilator like Albuterol.

Interpreting the Results

One of the main values your doctor will look at is your FEV1. The value is based on a percentage of what would be expected in the general population.

Based on that percentage, your doctor will be able to classify the level of lung obstruction caused by your asthma. The FEV1 values are broken down as follows:

  • FEV1 greater than 80 percent of predicted = Normal
  • FEV1 60 percent to 79 percent of predicted = Mild obstruction
  • FEV1 40 percent to 59 percent of predicted = Moderate obstruction
  • FEV1 less than 40 percent of predicted = Severe obstruction

If your doctor is unsure you have asthma, an improvement of 12 percent or more after using a rescue inhaler is enough to confirm the diagnosis.

Pros and Cons Home Spirometry

There are a number of reasons why you might want to purchase a home spirometry unit. Some people use it as a means to self-monitor their condition. Others buy one if they are uninsured, underinsured, or unable to afford the cost of a doctor visit.

With improvements in technology, home spirometry has become increasingly accepted by the medical community. Beyond convenience, a home device allows you to regularly monitor trends over periods of time and report back to your doctor. This alone can help inform treatment more dynamically than a single office test.

On the flip side, while costs have come down considerably, the accuracy of the devices can vary by brand, with some lower cost units delivering less accurate results.

As such, a home spirometer may provide more of a suggestive trend than an actual one, making it far less useful in a clinical setting. Some providers have also expressed concerns that home spirometers may be used as a substitute for regular doctor visits or encourage people to adjust treatment without input from their doctor.

If interested in a home spirometer, ask your doctor for recommendations or bring the device into the office so that it can be compared to the one your doctor uses.

View Article Sources
  • McLaughlin, M.; Rance, K.; and Stout, J. "Understanding Spirometry in Primary Care." Journal of Asthma and Allergy Educators. 2013; 4(6):282-289.