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Spirometry
Spirometry measures how much air a person can exhale and how quickly it leaves the lungs. It is central to many asthma evaluations but must be performed with acceptable technique and interpreted with symptoms.
Understanding Spirometry
Spirometry: what the first evaluation should clarify
What the test measures
Common values include forced vital capacity and the volume exhaled in the first second. The pattern can suggest airflow obstruction, restriction that needs confirmation, or a technically limited effort.
Bronchodilator response
When appropriate, spirometry is repeated after a bronchodilator to look for meaningful change. Improvement can support variable airflow limitation, while a normal result between episodes does not automatically exclude asthma.
Care Options
Preparing for reliable results
Follow the testing team’s instructions about inhalers, meals, clothing, smoking, and recent illness. Do not stop prescribed medicine based on general online advice. Bring every inhaler and spacer so technique and actual use can be reviewed.
Spirometry planning questions
Build the spirometry next step from evidence
Test quality changes the meaning
Spirometry depends on a complete breath in, a fast forceful start, continued exhalation, and repeatable efforts. Coaching and several attempts are normal. Pain, fatigue, language barriers, poor mouth seal, cough, or misunderstanding can make a technically limited result look like disease or hide an abnormality.
The report should indicate whether quality and repeatability criteria were met, not only list a percentage.
A normal result does not end every asthma evaluation
Asthma can vary over time, and baseline spirometry may be normal between episodes. Depending on the history, the clinician may compare results during symptoms, assess bronchodilator response, review peak-flow patterns, or consider exercise or other bronchoprovocation testing.
Conversely, obstruction is not specific to asthma. Age, exposure history, smoking or vaping, and other lung conditions influence interpretation.
Know the Next Step
Spirometry versus a complete pulmonary function test
Spirometry measures airflow and exhaled volume. A full pulmonary function laboratory may add lung volumes, diffusion capacity, or other measurements when the clinical question requires them. These services should not be presented as identical.
Ask which test was ordered, where it is performed, how medicines should be handled beforehand, and when the interpreted result will be reviewed with you.
Quality Comes Before Interpretation
Reliable spirometry depends on repeatable technique and clinical context
Spirometry is an effort-dependent test, so the tracing must meet quality criteria before the numbers are interpreted. The patient seals around the mouthpiece, inhales fully, then starts the exhalation forcefully and continues long enough to empty the lungs. Several attempts are usually needed. Coughing in the first second, a hesitant start, an early stop, a leak, or inconsistent effort can change the apparent pattern.
The report should be read as more than a percentage. Forced expiratory volume in one second, forced vital capacity, their ratio, the shape of the flow-volume loop, reference limits, repeatability, symptoms during testing, and recent medicine use all matter. A low ratio may support airflow obstruction; a reduced vital capacity can have several explanations and does not confirm restriction without the appropriate additional lung-volume assessment.
When bronchodilator testing is performed, the before-and-after change is interpreted with the starting values and the clinical question. A meaningful response can support variable airflow limitation, while a normal test between episodes does not rule out every form of asthma. The asthma evaluation guide explains when repeat testing, symptom correlation, or another objective method may be considered.
Questions About Spirometry
Frequently Asked Questions About Spirometry
Can spirometry be normal even if I have asthma?
Yes. Airflow can be normal between episodes or after treatment. A clinician may compare symptoms with prior results, repeat testing under appropriate conditions, or consider another objective test when the history remains convincing.
Should I stop my inhaler before spirometry?
Only follow the instructions provided for your specific test. The answer depends on whether the clinician wants to measure treated function, baseline function, or bronchodilator response. Do not stop prescribed medicine on your own.
Can spirometry diagnose restrictive lung disease?
Spirometry can show a pattern that raises the question, but restriction is generally confirmed with lung-volume testing. A reduced forced vital capacity may also reflect effort, air trapping, or another factor.
Can children perform spirometry?
Many school-age children can produce reliable results with coaching, and some younger children can as well. Interpretation depends on acceptable, repeatable maneuvers rather than age alone; an incomplete effort should not be treated as a definitive result.
Care Connected with Spirometry
Evaluation and treatment related to Spirometry
These diagnostic and treatment topics can shape a focused spirometry discussion.
Pulmonary Function Testing: What to Expect
Pulmonary Function Testing: What to Expect can clarify a separate question that often appears while evaluating Spirometry.
View guideAsthma Evaluation and Diagnosis
Use the Asthma Evaluation and Diagnosis guide to compare preparation, evidence, and next steps alongside Spirometry.
View guideExercise-Induced Asthma
Open Exercise-Induced Asthma for connected testing or treatment decisions that may follow a Spirometry discussion.
View guidePlan the next spirometry conversation
Bring the symptom, reaction, testing, and treatment records named in this Spirometry guide so the visit can answer a focused question.
Treatment directory
Compare treatment options
Return to the treatment directory to compare therapies, testing pathways, and the questions to discuss before scheduling.
