Passing a spirometry test comes down to two things: preparing properly beforehand and nailing the breathing technique during the test. The test itself is straightforward, but it requires a specific type of maximal effort that feels unnatural to most people. You’ll blow into a mouthpiece as hard and as long as you can, and the machine will measure how much air your lungs hold and how quickly you can push it out. Here’s how to give the test your best effort and get accurate results.
What the Test Actually Measures
Spirometry captures two key numbers. The first is your total lung capacity when you forcefully exhale, called FVC. The second is how much of that air you can push out in the first second, called FEV1. The ratio between these two numbers is what your doctor uses to evaluate your lung health. In healthy lungs, you can typically exhale 75% to 85% of your total air volume within that first second. A ratio of 0.7 or higher has traditionally been considered normal, though modern standards adjust for your age, sex, and height to avoid misdiagnosis.
Your individual results are compared against predicted values for someone of your same age, height, sex, and ethnicity. Historically, hitting 80% of your predicted value was considered the cutoff for normal. Current guidelines from the American Thoracic Society use a more precise statistical threshold that accounts for the natural decline in lung function as you age.
How to Prepare the Day Before and Day Of
If you use inhalers, the most important preparation step is knowing when to stop them. The withholding times vary significantly depending on the type:
- Short-acting inhalers (like albuterol): stop at least 6 hours before
- Short-acting anticholinergic inhalers (like ipratropium): stop at least 12 hours before
- Long-acting inhalers (like formoterol or salmeterol): stop at least 24 hours before
- Ultra-long-acting inhalers (like tiotropium): stop at least 36 hours before
These withholding times only apply if your doctor ordered pre- and post-bronchodilator testing. If you’re unsure, call the office that scheduled your test and ask. Never stop a prescribed medication without checking first.
Beyond inhalers, avoid smoking for at least one hour before the test and skip vigorous exercise for at least 30 minutes beforehand. Both can temporarily alter your airway function and skew results. Wear loose, comfortable clothing that doesn’t restrict your chest or abdomen, since you’ll need full range of motion in your torso. Avoid eating a large meal right before the test, as a full stomach pushes up against the diaphragm and limits how deeply you can inhale.
The Three Steps of the Breathing Maneuver
The forced expiratory maneuver has three distinct phases, and each one matters. Getting even one wrong can invalidate your results and force you to repeat the test.
Step 1: Inhale completely. Before you blow, you need to fill your lungs to absolute maximum capacity. This means breathing in until you physically cannot take in any more air. Most people underestimate how full they can get their lungs. Think of it as topping off a gas tank: keep sipping air in even after you think you’re done. The hesitation between finishing your inhale and starting your exhale should be two seconds or less, so once you’re full, move quickly to the next step.
Step 2: Blast the air out. The very first moment of your exhale is critical. You need to blow out as hard and as fast as physically possible, like you’re trying to blow out every candle on a birthday cake at once. This isn’t a steady breath out; it’s an explosive burst. A slow or hesitant start is one of the most common reasons tests get flagged as unacceptable. If air leaks out before your real effort begins, the machine detects it and the maneuver won’t count.
Step 3: Keep blowing until you’re completely empty. After that initial blast, keep exhaling steadily for as long as you can. The goal is at least 6 seconds of continuous exhalation, and the test isn’t considered complete until there’s almost no air coming out for a full second (a “plateau”) or you’ve been exhaling for 15 seconds. This is the hardest part. Most people feel like they’re out of air long before they actually are. Keep pushing, even when it feels like nothing is coming out.
Common Mistakes That Ruin Results
The technician needs at least three acceptable blows to complete the test, and several common errors will cause a maneuver to be thrown out. Knowing these in advance helps you avoid them.
Tongue or throat obstruction is surprisingly common. If your tongue drifts toward the mouthpiece or your throat tightens during the exhale, it creates a choppy, saw-tooth pattern on the readout that makes the data unusable. Keep your tongue below the mouthpiece and your throat open and relaxed, as if you’re fogging up a mirror.
Coughing during the exhale, especially in the first second, will invalidate that attempt. If you feel a cough coming, let it happen, recover, and try again. Closing your throat partway through (a reflex that feels like a tiny gulp or hiccup) also ruins the maneuver. So does stopping your exhale too early because you feel like you’re out of air.
Leaks around the mouthpiece are another frequent problem. Your lips need to form a complete seal around the mouthpiece with no air escaping from the corners of your mouth. Some people find it helpful to press the mouthpiece gently against their teeth and wrap their lips firmly over it.
What to Expect During the Test
You’ll be seated upright, and the technician will place a clip on your nose to make sure all air goes through your mouth. (Interestingly, research shows nose clips don’t significantly change the measured values for most people, but they’re standard practice because they eliminate one variable.) You’ll get a disposable mouthpiece attached to the spirometer.
The technician will coach you through every step, often with sharp, enthusiastic commands. This is intentional. Phrases like “Blast!” timed right at the moment you start exhaling help you overcome the natural tendency to hesitate. During the long exhale, they may count down (“two more seconds, one more second”) to motivate you to keep going. Some technicians will tell you to “suck in” your abdominal muscles near the end of the exhale to squeeze out the last bit of air. Follow their cues closely; experienced technicians know exactly how to get the best performance out of you.
Expect to repeat the maneuver at least three times, and possibly more if early attempts have technical problems. It’s normal to feel lightheaded or tired between blows. Take your time recovering between attempts. The test typically takes 15 to 30 minutes total.
If Your Test Includes a Bronchodilator
Many spirometry orders include a “pre and post” component. You’ll do the breathing test first, then inhale a short-acting bronchodilator (a medication that relaxes and opens your airways), wait about 15 minutes, and repeat the test. This tells your doctor whether any airflow limitation is reversible, which is a key distinction between conditions like asthma and chronic obstructive lung disease. The technique for both sets of blows is identical, so everything above applies to both rounds.
Conditions That May Postpone Your Test
Spirometry requires forceful effort that temporarily raises pressure in your chest, abdomen, and head. Certain conditions make the test unsafe. If you’ve had a recent heart attack, a pneumothorax (collapsed lung), a pulmonary embolism, or are coughing up blood, the test will be postponed. Recent surgery on your chest, abdomen, eyes, ears, or brain is also a reason to delay. A known large aortic aneurysm (over 6 cm) or significantly elevated blood pressure on the day of testing can also disqualify you temporarily. If any of these apply, let the testing facility know before your appointment so you don’t make an unnecessary trip.