What happens during an asthma test

Asthma is diagnosed through a combination of your medical history, a physical exam, and breathing tests. There is no single blood test or imaging scan that confirms asthma on its own. Instead, your doctor looks at your symptoms, listens to your lungs, and measures how well your airways work using a device called a spirometer.

The spirometer is the most common test. You breathe into a tube connected to a machine that measures how much air your lungs hold and how fast you can push air out. This takes about 15 minutes and is painless. Your doctor may also give you a medication to inhale and then repeat the test to see if your airways open up — this helps confirm asthma rather than another lung condition.

Not everyone needs every test. A child with clear asthma symptoms and a family history of asthma might be diagnosed after a physical exam and one spirometry test. An adult with a less obvious pattern might need additional tests to rule out other conditions.

Key Takeaways

  • Spirometry, a breathing test using a handheld device, is the standard way to measure how well your lungs work and is usually the first test your doctor orders.
  • Your doctor will ask about your symptoms, when they happen, and whether asthma runs in your family — this history is as important as the breathing test itself.
  • A positive spirometry result followed by improvement after inhaling a bronchodilator medication strongly suggests asthma.
  • Children under age 5 or adults with unclear symptoms may need additional tests such as a methacholine challenge or allergy testing.
  • Testing usually happens in your doctor's office or a pulmonology clinic and takes 30 minutes to an hour total.

The spirometry test and what the numbers mean

During spirometry, you sit in front of the machine and breathe normally for a few breaths. Then you take the deepest breath you can and blow out as hard and as fast as possible into the tube. The machine records two main numbers: how much air your lungs can hold (called FVC, or forced vital capacity) and how much air you can push out in the first second (called FEV1, or forced expiratory volume in one second).

Your doctor compares these numbers to what is normal for someone your age, height, and sex. If your FEV1 is lower than expected — usually below 80 percent of the predicted value — it suggests your airways are narrowed. This is the hallmark of asthma, but it can also point to other lung diseases.

That is why your doctor often gives you a short-acting bronchodilator (a medication that opens airways) and repeats the test 15 minutes later. If your numbers improve by 12 percent or more, it is a strong sign that asthma is the problem. If they do not improve, your doctor may order other tests or consider a different diagnosis.

Medical history and physical exam

Before any breathing test, your doctor will ask detailed questions about your symptoms. When do they happen — during exercise, at night, when you are around animals or dust? How often? Do you cough, wheeze, feel short of breath, or have chest tightness? Have you noticed a pattern, such as symptoms getting worse in winter or during allergy season?

Your doctor will also ask whether asthma, allergies, or eczema run in your family. Asthma has a genetic component, so a family history raises the likelihood. They will want to know about your job, your home environment, and any recent respiratory infections.

During the physical exam, your doctor listens to your lungs with a stethoscope while you breathe. In asthma, the airways are often inflamed and narrowed, which can produce a whistling sound called a wheeze. However, many people with asthma do not wheeze, and some people who wheeze do not have asthma. This is why the breathing test is so important — it gives an objective measurement rather than relying on what your doctor hears.

Additional tests when the diagnosis is unclear

If spirometry results are borderline or your symptoms do not fit the typical asthma pattern, your doctor may order a methacholine challenge test. You inhale a substance called methacholine, which irritates the airways of people with asthma and causes them to narrow. Your doctor then measures your lung function again. If your airways narrow significantly at a low dose of methacholine, asthma is likely. If they do not react, asthma is less probable.

For people with symptoms that seem linked to allergies — sneezing, itchy eyes, or a runny nose alongside respiratory symptoms — your doctor might order allergy testing. This can be a skin test (where small amounts of common allergens are pricked into your skin) or a blood test. Knowing your allergies helps your doctor understand what might be triggering your asthma.

In some cases, your doctor may order a chest X-ray to rule out other conditions like pneumonia, a collapsed lung, or heart problems that can mimic asthma symptoms. This is especially common if you have a fever, cough up blood, or have other warning signs.

Testing in children under 5

Young children cannot reliably perform spirometry because they cannot follow the breathing instructions. Instead, doctors diagnose asthma in this age group based almost entirely on symptoms and response to treatment. A doctor will ask about coughing, wheezing, or shortness of breath, especially during play, sleep, or after illness.

If a young child has symptoms that sound like asthma, the doctor may prescribe a trial of asthma medication — usually an inhaler with a spacer (a tube that makes it easier for small children to receive the medication). If the symptoms improve, asthma is likely. If they do not, the doctor will look for other causes.

Once a child reaches age 5 or 6, spirometry becomes possible, and your doctor may order it to confirm the diagnosis or to measure how well treatment is working.

What to expect on the day of your test

Wear loose, comfortable clothing that does not restrict your chest or belly. Avoid caffeine for 4 hours before the test, as it can affect your breathing. If you use a rescue inhaler, ask your doctor whether to use it before the test — usually you should not, because the test measures your baseline lung function.

Bring a list of all medications and supplements you take, including over-the-counter ones. Some medications can affect spirometry results. Plan to spend 30 minutes to an hour at the clinic. The test itself is quick, but there is paperwork and waiting time.

During the test, the technician will give you clear instructions and may demonstrate the breathing technique. It is normal to feel lightheaded or tired after blowing hard into the spirometer. Drink water afterward and rest if you need to. You can drive and return to normal activities immediately after.

After testing: what happens next

Your doctor will review the results with you, usually within a few days. If the results confirm asthma, your doctor will discuss a treatment plan. This typically includes a rescue inhaler (for sudden symptoms) and often a controller medication (taken daily to prevent symptoms). Your doctor will show you how to use your inhaler correctly, as many people do not use them properly.

If results are unclear, your doctor may repeat testing in a few weeks or order additional tests. Sometimes asthma develops gradually, and a single negative test does not rule it out forever. If your symptoms continue, mention this at your next visit.

Once you have been diagnosed, you will not need spirometry every visit. However, your doctor may repeat it yearly or when your symptoms change, to track how well your treatment is working and whether your lung function is stable.

Frequently Asked Questions

Can asthma be diagnosed without a spirometry test?

In young children and in some adults with very clear symptoms and a strong family history, yes. However, spirometry is the standard because it provides objective evidence. Without it, other conditions can be mistaken for asthma, leading to wrong treatment.

Is spirometry safe if I am having an asthma attack?

No. Do not have spirometry during an active attack or if you are wheezing heavily. Wait until your symptoms are controlled. If you are having trouble breathing, tell your doctor before the test — they may reschedule or give you medication first to open your airways.

What if my spirometry results are normal but I still have symptoms?

Normal spirometry does not completely rule out asthma. Some people have asthma that only shows up during exercise or after exposure to a trigger. Your doctor may order a methacholine challenge test or ask you to keep a symptom diary to capture when symptoms occur, then retest at that time.

How long does it take to get results?

The spirometer produces results immediately, and your doctor can often discuss them with you the same day. If additional tests are ordered, results may take a few days to a week depending on the test and the clinic's schedule.

Will I need to repeat testing after I start asthma medication?

Your doctor may repeat spirometry a few weeks after starting treatment to see whether your lung function has improved. After that, testing is usually done yearly or when symptoms change, not at every visit.