Spirometry

What Spirometry Measures

Spirometry is one of the most common breathing tests used to evaluate how well the lungs are moving air. During the test, you breathe into a mouthpiece connected to a device called a spirometer, which records how much air you exhale and how quickly you exhale it. The results are usually reported as a few key numbers you may see on your printout.

FVC (Forced Vital Capacity)

The total amount of air you can forcefully exhale after taking as full a breath in as possible. It reflects the overall volume of air your lungs can move during a forceful breath out.

FEV1 (Forced Expiratory Volume in One Second)

The portion of that air you're able to exhale during just the first second of the effort. Because airway narrowing tends to slow airflow early in an exhale, FEV1 is especially useful for assessing how freely air is moving out of the lungs.

FEV1/FVC Ratio

The fraction of your total exhaled air that came out in that first second, comparing FEV1 to FVC. This ratio is one of the values clinicians look at when considering whether airflow is obstructed.

Each of these values is also expressed as a percentage of what would be expected for someone of your age, height, sex, and sometimes ethnicity, since normal lung capacity varies from person to person.

The Flow-Volume Curve

What a Reduced FEV1/FVC Ratio Can Suggest

What Happens During the Test

1. 01→Full Breath InYou take as full a breath in as possible before the maneuver begins.↓
2. 02→Forceful, Complete ExhaleYou exhale into the mouthpiece as forcefully, completely, and steadily as you can, which takes real effort and coordination.↓
3. 03Repeated AttemptsTechnicians typically ask you to repeat the maneuver multiple times to confirm your results are reproducible. The most consistent, technically acceptable efforts are used for the final report; if your results vary widely between attempts, you may be asked for additional tries.↓
4. 04→Bronchodilator (If Ordered)You may be given an inhaled bronchodilator medication and asked to wait about fifteen minutes.↓
5. 05Repeat After BronchodilatorThe breathing maneuver is repeated so your care team can see whether your airflow improves meaningfully after the medication.

A significant improvement in airflow after the bronchodilator supports the possibility of a reversible, asthma-type component to your breathing pattern. This response is one piece of information among several: it does not, by itself, confirm an asthma diagnosis, and its absence does not rule one out. Your physician weighs the bronchodilator response alongside your other results and clinical history.

Preparing for the Test

Because certain factors can affect how your lungs perform on the day of testing, your care team may give you specific preparation instructions. These commonly include:

• Avoiding a heavy meal before the test
• Avoiding vigorous exercise before the test
• Avoiding smoking for a period of time before the test
• Possibly holding certain inhaled medications beforehand so they don’t mask your baseline results

These are general categories of guidance, not a substitute for your own physician’s instructions. Always follow the specific preparation directions given by the office that ordered your test, since they may differ based on why the test was ordered and what medications you take.

If you’re unsure whether to take your usual inhaler or other breathing medication on the morning of your appointment, it’s reasonable to call the ordering office ahead of time rather than guess. Skipping a dose you actually need, or unexpectedly taking one you were asked to hold, can both affect how your results should be interpreted.

What Spirometry Results Can and Cannot Tell You

Spirometry provides objective, measurable information about airflow that supports the diagnosis and ongoing monitoring of conditions such as asthma and COPD. It is a core part of how COPD is diagnosed and staged, and it plays an important supporting role in asthma evaluation, particularly when combined with bronchodilator response testing.

At the same time, spirometry results are one part of a broader clinical evaluation. They are always interpreted together with your symptoms, physical exam, medical history, and sometimes additional testing. Spirometry alone does not deliver a stand-alone diagnostic verdict, and no single value from the test, including the FEV1/FVC ratio, should be used to self-diagnose a breathing condition.

Where Spirometry Fits Within Pulmonary Function Testing

Spirometry may also be paired with other pulmonary tests, such as feno testing, depending on what your care team is trying to evaluate. Reviewing your spirometry results together with any related testing gives your physician a more complete view than any single test could provide on its own.