Preparing for a pulmonary function test (PFT) mostly comes down to what you avoid in the hours before the appointment. The biggest factors are temporarily stopping certain inhaler medications, skipping cigarettes and caffeine, eating lightly, and wearing the right clothing. Getting these details right helps ensure your results accurately reflect how your lungs are actually working.
A PFT is a group of breathing tests that measure how much air your lungs can hold, how quickly you can move air in and out, and how well your lungs transfer oxygen into your blood. You’ll breathe into a mouthpiece connected to a machine, sometimes gently and sometimes with maximum effort. The whole process typically takes 30 to 90 minutes depending on which tests your doctor ordered.
When to Stop Inhaler Medications
If you use inhalers, you’ll likely need to hold off on them before the test. The reason is straightforward: bronchodilators open your airways, and the test needs to capture your baseline lung function before any medication effect. The withholding window depends on how long your inhaler lasts.
- Short-acting rescue inhalers (albuterol, salbutamol): stop 6 hours before
- Short-acting anticholinergic inhalers (ipratropium): stop 12 hours before
- Long-acting inhalers (formoterol, salmeterol): stop 24 hours before
- Ultra-long-acting inhalers (tiotropium, indacaterol, vilanterol): stop 36 hours before
If you’re scheduled for a methacholine challenge test, which checks for airway hyperreactivity, the withholding times are even longer. Short-acting rescue inhalers still require 6 hours, but long-acting versions need 36 hours, ultra-long-acting types need 48 hours, and certain long-acting anticholinergic medications may need to be stopped a full week (168 hours) in advance.
These timelines come from the NIH’s pulmonary function lab and align with guidelines from the American Thoracic Society and European Respiratory Society. Your doctor’s office should tell you exactly which medications to pause and when. If they don’t bring it up, ask. And importantly, only stop medications you’ve been told to stop. Continuing steroid inhalers or other controller medications is often fine, but confirm with your care team.
Food, Caffeine, and Smoking
Avoid eating a large meal for at least two hours before your test. A full stomach pushes up on your diaphragm and can reduce how much air your lungs take in, which means your results won’t reflect your true capacity. A light snack is generally fine.
Skip caffeine on the day of your test. Coffee, tea, energy drinks, and sodas with caffeine can all affect airway tone and potentially alter your results, particularly if you’re having a bronchial challenge test.
If you smoke, stop for at least 4 to 6 hours before the test. Smoking temporarily narrows your airways and increases carbon monoxide levels in your blood, both of which skew results. The longer you can go without smoking before the appointment, the more accurate the picture.
What to Wear
Wear loose, comfortable clothing that doesn’t squeeze your chest or abdomen. Tight waistbands, compression garments, and restrictive bras can physically limit how deeply you inhale. You’ll be asked to take the deepest breaths you possibly can during several parts of the test, so anything that restricts your rib cage or belly expansion works against you. Think of what you’d wear to a casual doctor’s visit: a loose-fitting shirt and pants with a comfortable waistband.
Exercise and Physical Activity
Avoid heavy exercise before your test. Vigorous activity changes your breathing patterns, heart rate, and airway dynamics in ways that can linger for hours. A calm walk to the parking lot is fine, but skip your morning run or gym session. Plan to arrive a few minutes early so you can sit and relax before the test begins.
Recent Surgeries or Medical Events
Certain medical situations mean your PFT should be postponed. The highest-risk scenarios include a recent heart attack, a blood clot in the lungs, or a known expanding aortic aneurysm. These are situations where the forceful breathing required during the test could be dangerous.
Recovery from major chest, abdominal, or head surgery also requires a waiting period. The traditional recommendation was six weeks, but with modern, less invasive surgical techniques, many patients can safely test within three weeks. If you’ve had any surgery or major medical event in the past month, let the testing facility know ahead of time so they can determine whether it’s safe to proceed.
What the Test Feels Like
The test itself is noninvasive and painless, but it does require real physical effort. You’ll wear a nose clip and breathe through a mouthpiece. Some maneuvers ask you to blast air out as hard and fast as you can, which can feel intense. Others require slow, steady breathing. A technician will coach you through each step and may ask you to repeat certain maneuvers several times to get consistent readings.
It’s normal to feel lightheaded, slightly short of breath, or tired during or right after the test. These sensations usually pass within a few minutes. If you have a bronchodilator reversibility test, you’ll use a rescue inhaler partway through and then repeat some of the breathing maneuvers to see how your lungs respond. In that case, you might notice a mild tremor or increased heart rate from the medication, which is temporary.
You can return to all your normal activities, including driving, immediately after the test. Resume any medications you paused as soon as the testing is complete, unless your doctor tells you otherwise.
Quick Prep Checklist
- Inhalers: Stop according to the schedule your doctor provides (6 to 36+ hours depending on type)
- Food: No large meals for 2 hours before; light snacks are okay
- Caffeine: None on the day of the test
- Smoking: None for at least 4 to 6 hours before
- Exercise: No vigorous activity the morning of the test
- Clothing: Loose and comfortable, nothing tight around the chest or waist
- Arrive early: Give yourself a few minutes to sit and relax before testing begins