What Is Spirometry?

What to expect when undergoing this test

Man using a spirometer
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Spirometry is a type of pulmonary function test (PFT), a noninvasive procedure that provides important information about how well the lungs are working. More specifically, it reveals how much air is moving through the lungs and how quickly as you breathe through a tube. The test is used to diagnose respiratory conditions such as asthma and to monitor lung diseases in order to evaluate how well treatment is working. Sometimes spirometry is done in conjunction with other PFTs, depending on the specific information a doctor is looking for.

Purpose of Test

Spirometry measures key aspects of lung function. The test can play an important role in diagnosing and managing many lung problems. It can be used to distinguish between diseases that appear similar based on symptoms alone. Spirometry is also useful for evaluating how a lung disease is progressing (is it getting better, worse, or staying the same?), which can help to indicate if a current treatment plan is working or needs to be modified.

Spirometry is rarely used alone to diagnose a lung condition, however. It usually is combined with other findings, such a medical history, physical examination, and imaging tests. Spirometry may be used to help diagnose:

The procedure also may be done before lung cancer surgery to provide information to the surgeon about how well a patient is likely to tolerate an operation from a respiratory standpoint, as well as how that person might respond to having a portion of or a whole lung removed.

Research has found that spirometry can be useful for predicting lung cancer in workers and others who've been exposed to asbestos. In fact, a 2017 study found that spirometry was so useful for this purpose the scientists recommended the test be offered to all workers who have had asbestos exposure and be repeated every three years.

Risks and Contraindications

Spirometry is a very safe procedure, but you may become short of breath or feel a little lightheaded while taking deep breaths during the test. You might also experience some coughing.

People with asthma are at a small risk of having an asthma attack during a spirometry test. In very rare instances, the exertion can cause a person to develop severe breathing problems temporarily.

Contraindications

It's not recommended that people have a spirometry test if they:

  • Have chest pain or have recently had a heart attack or stroke
  • Have a collapsed lung (pneumothorax)
  • Have recently had eye surgery, as the deep breathing required for spirometry can increase the pressure inside the eyes
  • Recently had abdominal or chest surgery
  • Have an aneurysm (bulging blood vessel) in the chest, abdomen, or brain
  • Have tuberculosis (TB)
  • Have a respiratory infection, such as a cold or the flu

There are certain conditions under which a person may not be able to breathe as fully and deeply as required, which can make affect the accuracy of a spirometry test. These include:

  • Pregnancy
  • Stomach bloating
  • Extreme fatigue
  • General muscle weakness

Before the Test

Being aware of what's involved in a spirometry test and how best to prepare can help you get the most accurate results.

Timing

A spirometry test typically takes 40 to 45 minutes. Ask your doctor if you should plan to spend significantly more time than this so that you can schedule the rest of your day accordingly.

Location

Spirometry is usually done in the office of a pulmonologist, a doctor who specializes in lung health, or at a hospital as an out-patient procedure (meaning you go home afterward). An overnight hospital stay may be necessary, but only if the test is part of a more extensive test or procedure, such as lung surgery. Most of the time spirometry, is performed by a pulmonary function technician or a respiratory therapist.

At-home spirometry testing equipment is available, but is typically only recommended for use in certain cases (see below).

What to Wear

Because you will need to take very deep breaths, you should dress in clothing that won't restrict your breathing. For instance, you may not want to wear a belt or clothing that fits tightly around your waist.

Food, Drink, and Medications

There are a few things to keep in mind in this regard:

  • Eat lightly. If your stomach is too full, it may be hard for you to take deep-enough breaths.
  • Do not drink alcohol before the test. You may not be able to breathe as well if you have alcohol in your system, which could have a negative impact on your results.
  • If you take medication, make sure your doctor knows what it is. Certain drugs can affect breathing, particularly inhaled drugs such as bronchodilators. The American Lung Association says that if you have a short-acting inhaler you only use as needed, do not use it for six to eight hours prior to testing, if possible.

Cost and Health Insurance

For people with health insurance, a spirometry test that's considered medically necessary will be covered at 80 percent to 100 percent, depending on the terms of your policy and how much of your deductible you've met. You also may be responsible for a co-pay or coinsurance.

If you don't have health insurance, your out-of-pocket cost for a spirometry test can range from around $30 to more than $300, depending on the region of the country you're in when you have the test and other factors, according to the Healthcare BlueBook. The average cost of spirometry is around $54, but be aware that this does not include the cost of an office visit, which could add $25 to $100 (or more) to the total cost.

What to Bring

Aside from your insurance card to present at check-in, you shouldn't need to bring anything in particular to a spirometry test. To make sure, ask your doctor.

Other Considerations

Here are a few other things you should do before having a spirometry test that will help you breathe as fully as possible and get the most accurate results:

  • Go to bed early enough to get plenty of sleep the night before the test.
  • Do not smoke for at least four to six hours before the test. Lighting up may impact your results.
  • Don't do any heavy exercise or vigorous activity for at least 30 minutes before the test. It's important to conserve your energy.

During the Test

Here is a step-by-step description of what you are most likely to experience during a spirometry test, keeping in mind that there can be differences among individual practitioners in how the procedure is carried out. Your doctor can be more specific about what to expect.

Pre-Test

After you arrive for your appointment, you will check in. This may involve filling out forms, including a consent form, having your insurance card photocopied for your files, and taking care of your co-pay if you have one.

When you are called for your test, you will be asked to empty your bladder. You then will be escorted to the room where the spirometry will take place. The technician or respiratory therapist administering the test will weigh and measure you or ask for your height and weight. Be truthful: Spirometry results are calculated based on what's normal for someone who's the same height, weight, age, and gender as you; sometimes ethnicity is factored in.

You'll be instructed to loosen your belt and remove any clothing or jewelry that might restrict your breathing. If you wear dentures, you will leave them in for the test.

Throughout the Test

During the test, you will be seated in a chair. You may be told to sit and just breathe normally for a while. To prepare you for the test, the technician will put a clip on your nose to keep it gently closed so that you do all of your breathing through your mouth.

In most cases, you'll then be given a small piece of equipment that you can hold in your hand. It will have a sterile mouthpiece that's connected to the spirometer, a machine that's roughly the size and shape of a home printer. The machine will register the force of your breath and create a printout of the results.

You may encounter another type of spirometer if your doctor's office doesn't have a regular one or if you're not able to move to a different room. These are portable—the mouthpiece is connected directly to a small handheld device about the size of a point-and-shoot camera that will display your results or send them wirelessly to a computer or printer.

The therapist will give you very specific instructions on how to hold the equipment and place your lips around the mouthpiece to create a tight seal so that air doesn't escape. Once you've mastered this, you will be told to take in as big and deep a breath as you possibly can and to then blow it out as hard and fast as you can. It's vital that you use maximal effort and that you empty your lungs completely. You'll do this at least three times. The technician will be right there to talk you through each step.

The spirometer will create a graph that depicts your results and that the technician can read and interpret on the spot. In some cases, if a person's breathing patterns show an obstruction, he will be asked to use a short-acting bronchodilator such as albuterol to help open the airways and then repeat the test to see if the medication brings about an improvement.

Post-Test
After a spirometry test, you can return to your normal activities. You also can go back to taking any medications you were asked to stop for the test.

Interpreting Results

Since the results of your test will be ready immediately, it's likely your doctor will review and discuss the results with you at your appointment. To do that, he will go through a standard procedure for reading spirometry tests.

The first step is to make sure the test was valid. This is important because there are a number of things that can go wrong during the test that can cause spirometry results to be inaccurate:

  • The person wasn't able to put enough effort into breathing into the machine (often due to illness or pain that worsens with each breath)
  • They didn't fully understand the test instructions (possibly due to a language or cognitive barrier, or hearing loss)
  • Coughing during the inhale or exhale
  • The person didn't create an adequate seal around the spirometer mouthpiece, or their tongue or teeth were incorrectly placed in front of the mouthpiece
  • There was a deformation of the mouthpiece caused by biting or chewing

To be considered accurate, your test must not have been impacted by these issues and your results must have been able to be reproduced. That's why you'll be asked to repeat the test a minimum of three times.

Spirometry provides two important measurements of lung function:

To meet reproducible criteria, all three FEV1 measurements and all three FVC measurements must be within 200 milliliters (ml) of each other. If any of these conditions aren't met, the test has failed to meet the reproducibility criteria and the doctor will decide if it should be repeated and when.

When the doctor is satisfied that the test is valid, he will decipher the information on the printout.

The greatest FEV1 and FVC measurements achieved represent the patient's results for the entire test. The doctor will consider these individual numbers and calculate the ratio of FEV1 to FVC to determine if your spirometry is normal or abnormal.

Abnormal results indicate one of three possible breathing patterns:

Obstructive: When the airways are narrowed (obstructed), the amount of air you can blow out quickly in one second (FEV1) is less than would be expected based on your age, height, and weight. Put another way, obstructive lung diseases cause the lungs to take in too much air and take too long to empty. Since your FEV1, in this case, is low, the ratio of FEV1/FVC will be lower than average. An obstructive pattern will be seen in lung conditions affecting the airways such as COPD and asthma.

The FEV1 values are broken down as follows:

  • FEV1 greater than 80 percent of predicted is normal
  • FEV1 60 percent to 79 percent of predicted indicates mild obstruction
  • FEV1 40 percent to 59 percent of predicted indicates moderate obstruction
  • FEV1 less than 40 percent of predicted indicates severe obstruction

Restrictive: A restrictive pattern will be indicated by a low FVC, but a normal ratio of FEV1 to FVC (meaning both numbers are proportionately decreased). Restrictive lung disease is sometimes associated with chest surgery (after a lumpectomy to treat breast cancer or a pneumonectomy, which is the removal of all or part of a lung); obesity; scoliosis (curvature of the spine); sarcoidosis (inflammation of the lymph nodes, lungs, liver, or other tissues); and scleroderma (a buildup of scar tissue in the skin and other parts of the body). A restrictive lung problem means lungs contain too little air and do a poor job of transferring oxygen into the blood.

Combination: A combination of both breathing patterns may be seen when a person has more than one lung disease—cystic fibrosis and asthma, for example.

If you went through a second round of testing after using a bronchodilator and your numbers improved by 12 percent or more, this is confirmation that you have asthma. If you have COPD, the results of a spirometry test after using a bronchodilator can also indicate how severe your disease is.

Follow-Up

If your spirometry test alone doesn't determine with certainty that you have an obstructive or restrictive lung disease; a combination of two conditions; or what your exact diagnosis is, your doctor may order other pulmonary function tests, such as plethysmography that can measure total lung capacity.

However, if your doctor is able to come up with a specific diagnosis based on your spirometry test, then the next step will be to discuss treatment—which could include anything from medication for asthma to a lung biopsy if there's the possibility of cancer.

Home Spirometry

A home spirometry unit—which basically is a scaled-down version of the type of machine used in a clinical setting—can be useful under certain conditions with the oversight of a doctor, and your doctor may recommend using one after you get your in-office test results. A home device allows you to regularly monitor trends in your breathing patterns over a period of time to report back to your doctor, for instance. This information may help the doctor to fine-tune your treatment more dynamically than with the results of a single office test. (Note that there is a simpler type of spirometer called an incentive spirometer that does not provide measurements of lung function. It's a device designed to help keep a person's lung clear after surgery.)

In fact, there is increasing interest in using home spirometry to manage lung disease. For example, a 2017 study found that using home spirometry for the monitoring of complications after lung transplant surgery may be beneficial, but more research is needed. Another study explored home spirometry for people with cystic fibrosis and found that it could help identify a decline in lung function or exacerbation of the disease that would prompt early treatment that could "slow lung function decline, reduce respiratory symptoms, and improve the quality of life."

On the flip side, the accuracy of home spirometry devices can vary by brand. What's more, cheaper ones tend to deliver less accurate results. As such, a home spirometer may provide more of a suggestive trend than an actual one. Some doctors also have 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.

Only use a home spirometer if your doctor recommends it. Make sure you understand how to correctly use the unit you purchase and that you follow your doctor's instructions for reporting results accurately. You may even want to ask your doctor to recommend a unit he trusts.

A Word From Verywell

If you have had a spirometry, take a moment to have your doctor explain your numbers, as well as any change in your numbers over time. Being your own advocate and learning about your condition puts you in the best position to make sure you are getting optimal treatment and doing all you need to do to live your best life with your condition.

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