Pulmonary Function Testing: What to Expect

Tests Answer Different Questions

Spirometry, Bronchodilator Response, Lung Volumes, and Diffusion Testing

Airflow and bronchodilator response

Pulmonary function testing is an umbrella term. Depending on the clinical question and what is available at the testing location, an order may include one or more measurements:

Spirometry: measures how much air you can exhale and how quickly you can exhale it.
Bronchodilator responsiveness testing: repeats spirometry after an inhaled medication to measure a change in airflow.
Lung-volume testing: measures the amount of air in the lungs at different stages of breathing.
Diffusing-capacity testing: evaluates how gases move from the lungs into the bloodstream.

Volume and gas-transfer measurements

Confirm which measurements are included when scheduling your appointment.

Woman reviewing a breathing care plan for asthma relief.

A Repeatable Breathing Maneuver

What Happens During Spirometry

For spirometry, you will usually wear a nose clip and seal your lips around a clean mouthpiece. After taking a full breath, you will blow out as hard, fast, and completely as possible.

The test is repeated so the clinical team can confirm that the measurements are consistent and technically acceptable. Coaching is an important part of the test, and it can take practice to perform the maneuver correctly.

When bronchodilator testing is ordered, you may inhale a breathing medication and repeat the measurements after the required waiting period.

Protect Test Reliability

How to Prepare for Reliable Pulmonary Function Results

Follow medication instructions

Follow the instructions supplied for your specific appointment. Ask whether any inhalers should be withheld and for how long. Do not stop a prescribed breathing medication unless the ordering clinician tells you to do so.

For more reliable measurements, you may be instructed to:

Food, exercise, clothing, and records

avoid smoking before the test;
avoid strenuous exercise for at least 30 minutes;
avoid a large meal for about two hours;
avoid alcohol before testing;
wear clothing that does not restrict a deep breath; and
bring a complete medication and inhaler list.

Tell the office if you have a cold, flu, or other respiratory infection because the appointment may need to be rescheduled.

Patterns, Not One Number

How Clinicians Interpret Pulmonary Function Patterns

Spirometry commonly reports forced expiratory volume in one second, forced vital capacity, and their ratio. Results are compared with appropriate reference values and evaluated for technical quality.

An abnormal pattern can support the presence of airflow obstruction, possible restriction, or another physiologic change. Pulmonary function measurements alone do not identify one specific disease. Your clinician considers test quality, biological variability, symptoms, prior results, examination, and other diagnostic information.

Normal baseline spirometry does not always rule out asthma. FeNO testing, repeated spirometry, or a bronchial challenge may be considered when clinically appropriate.

Safety Before Testing

When Illness or Recent Procedures May Change the Test Plan

Tell the team before testing if you recently had:

a heart attack or unstable chest pain;
eye, ear, sinus, chest, or abdominal surgery;
a collapsed lung;
coughing of blood;
fainting triggered by forceful breathing; or
a contagious respiratory infection.

Forceful breathing can briefly cause coughing, fatigue, or lightheadedness. Stop the maneuver and tell the staff immediately if you develop chest pain, severe shortness of breath, dizziness, or feel faint.

Severe Symptoms Need Care

When Severe Breathing Symptoms Need Emergency Care

Pulmonary function testing is not an emergency evaluation. Call 911 for severe current breathing difficulty, blue or gray lips, confusion, fainting, severe chest pain, or symptoms that do not improve with prescribed rescue treatment.

Connect the Results

How PFT Results Fit With FeNO and Asthma Evaluation

Lung function testing is interpreted together with symptoms, examination findings, medication use, and the clinical question. Learn more about asthma evaluation, how FeNO testing answers a different question, and the elements of an individualized asthma treatment plan. A clinician should decide whether any of these evaluations are suitable and how to prepare.

Patient Questions

Frequently Asked Questions

Is spirometry the same as a full pulmonary function test?

Spirometry is the most common pulmonary function test, but a broader PFT evaluation may also include lung volumes or diffusing capacity. Ask which measurements your appointment includes.

Should I stop my inhaler before testing?

Only when the ordering clinician provides specific instructions. The correct withholding period depends on the medication and the purpose of the test.

Can normal spirometry rule out asthma?

No. Some patients with asthma have normal spirometry between episodes. Your clinician may use symptom history, bronchodilator testing, FeNO, peak-flow monitoring, or another test when needed.

Why do I have to repeat the breathing maneuver?

Several acceptable efforts help confirm that the result is reproducible and reflects your best performance rather than technique or an incomplete breath.

How long does pulmonary function testing take?

It depends on which tests were ordered and whether bronchodilator measurements are included. The scheduling team should provide an estimate for your specific appointment.

Related Care Guides

Prepare for reliable pulmonary function testing

Follow the ordering team’s instructions, bring every inhaler, and use the clinic directory to confirm the appointment.

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