What Is a Pulmonary Function Test? What to Expect at Your In-Office PFT.

If you have been told you need a pulmonary function test, it likely means your doctor wants to measure how your lungs are actually working, not just how you describe them as working. Symptoms are the starting point in any pulmonary evaluation, but they are unreliable on their own. Some people downplay what's limiting them because they've adjusted to it; others feel changes long before a test will pick them up. PFT exists to put objective numbers on what the lungs can do.

What a PFT actually measures

The test most people have heard of is spirometry. Spirometry asks a simple question with a hard-to-fake answer: how much air can you move out of your lungs, and how fast? The two key numbers are the forced vital capacity (FVC), which is the total amount of air you can exhale after a full inhalation, and the forced expiratory volume in one second (FEV1), which is how much of that air comes out in the first second. The ratio between them tells your clinician whether airflow obstruction is the main issue.

Beyond spirometry, depending on what your clinician is looking for, additional testing may include lung volume measurements (how big are your lungs?) and diffusion capacity (how well does oxygen actually cross from your lungs into the bloodstream?). Pre- and post-bronchodilator testing, performing spirometry, giving an inhaled medication, and then repeating the test, is often the test that confirms or rules out asthma.

What the test feels like

You'll sit upright, wear a nose clip, and be coached through a series of breathing maneuvers. The most physically demanding part is the forced exhalation: a deep breath in, then blow out as hard and as long as you possibly can into a mouthpiece. The technician will cheer you through it. We typically repeat the maneuver several times to get a reliable, technically acceptable result.

The test is not painful. It is tiring. Most patients are surprised at how much effort a full forced exhalation actually requires, and we build in rest breaks. A complete PFT visit usually runs roughly 30 to 60 minutes.

How to prepare

On the day of your test, avoid smoking for at least an hour beforehand if you smoke. Skip heavy meals immediately before. Wear comfortable, loose clothing that doesn't restrict your chest. Whether to hold inhalers ahead of the test depends on the question being asked, we'll give you specific instructions when we schedule your appointment.

Why in-office PFT matters

Performing the test in the same clinic where you're being treated shortens the loop. Results are interpreted the same day in many cases, the documentation lives in your chart immediately, and there is no multi-week relay between separate facilities. For DOL/OWCP and DEEOIC patients, in-office PFT also means the technical quality, the measured and predicted values, and the clinical interpretation arrive together as one coherent report, which is exactly what claims examiners need.

For more on the in-office PFT program, see our PFT page. For the broader pulmonary program, see pulmonology. Energy-sector patients filing under EEOICPA can find more on our DEEOIC page.

After the test

Your pulmonologist will walk you through what the numbers mean in plain language: what's normal, what isn't, what the test confirms or rules out, and what comes next. The point of doing the test is to act on the result, to choose the right treatment, the right follow-up interval, and the right documentation.

This article is for general information and is not medical advice. Talk to your clinician about whether PFT is appropriate for you.