To diagnose asthma, your doctor will likely perform breathing tests known as pulmonary function tests.

If you’re having trouble breathing — and especially if your breathing troubles are accompanied by wheezing and chest tightness — your doctor may suspect that you have asthma. (Or if you notice those symptoms yourself, that’s reason enough to see your doctor and ask if it might be asthma.)

It’s likely that your doctor will perform a number of tests before making a diagnosis. And it may be necessary for you to visit an allergist, pulmonologist, or other specialist to determine whether asthma is the cause of your symptoms.

“Asthma exists in many forms, including allergic asthma, exercise-induced asthma, and work-related asthma,” says Chitra Dinakar, MD, chief of allergy, asthma, and immunodeficiency at Stanford Health Care in California, and a spokesperson for the American College of Allergy, Asthma, and Immunology. “Each type can have different triggers and symptoms, and each requires a different approach to diagnosis and treatment.”

When Diagnosing Asthma, Medical Histories, Physical Exam, and Lung Function Tests Come First
Whether you’re visiting your primary care physician or a specialist, your doctor will likely take your personal and medical history, perform a physical exam, and take a lung function test to determine if asthma is the cause of your symptoms. These steps involve:

A personal and medical history Personal and medical histories will include questions about your symptoms, when they occur, how long you’ve been dealing with them, if anything has made you feel better or worse, and whether any one in your family tree had asthma or breathing problems. It’s helpful to your doctor if you keep a log or journal of your symptoms. Also, take some time to think (or find out) about your family history, before your appointment.

A physical exam Your doctor will listen to you breathe and listen to your heart (to rule out heart problems as the cause of your wheezing). He or she will also examine your nose, mouth, and ears for signs of inflammation or irritation, which could signal either asthma or the presence of some other ailment. Your doctor will also check your skin for rashes, and signs of eczema, which causes redness and dryness and is associated with both allergies and asthma.
A pulmonary function test There are several different breathing tests, also known as pulmonary function tests (PFTs, or lung function tests), that a doctor may use to diagnose asthma. Types of lung function tests are detailed in the next section.

There Are a Few Different Types of Lung Function Tests
The breathing tests your doctor may use to help determine if you have asthma include:

Spirometry This is the standard test to diagnose asthma. In this simple breathing test, you breathe into a mouthpiece connected to a device called a spirometer. This device measures the amount of air you're able to exhale and inhale, as well as how fast you can blow the air out. These measurements provide information about the narrowing of your bronchial tubes.

Peak airflow This test involves breathing into a peak-flow meter, a small, handheld device that measures the maximum force of air you can blow out. This test measures any narrowing of the airways, and can catch narrowing hours or potentially days before you experience asthma symptoms. (After being diagnosed, your doctor may recommend that you use a peak-flow meter at home to help figure out whether your condition is getting better or worse over time and whether or not your asthma management plan is working.)

Exhaled nitric oxide Your body normally produces nitric oxide, and research has shown that this gas is an indicator of inflammation. So, this test can help determine how much inflammation is present in your lungs. (Asthma is an inflammatory process; so increased inflammation in the lungs is potentially a sign of asthma.) For this test, you’ll exhale into a small, handheld machine for 10 seconds at a steady pace. The machine will calculate the amount of nitric oxide in your breath.

Inhalation challenge tests These tests measure your physical reaction to breathing in the drugs methacholine or mannitol, which are known to be asthma triggers. You’ll inhale an increasing amount of one of these drugs, and your lung function will be measured after each amount is administered. The test is considered positive if your lung function drops significantly.

Other Tests Can Be Helpful in Diagnosing Asthma, Too

Depending on your asthma symptoms or triggers, your doctor may also order or perform other tests in order to confirm or rule out whether asthma is the cause of your breathing issues.

These other tests can include:

Imaging tests Your doctor may order a chest X-ray or computerized tomography scan of your lungs and sinuses to look for signs of infection or other abnormalities.

Allergy tests These tests typically involve seeing how your skin reacts to a potential allergen and can help determine whether your symptoms are allergy related. This can also be determined by blood work.

Tests for other conditions Your doctor may look into whether you have another condition that can worsen your asthma or causes asthma-like symptoms, such as gastroesophageal reflux disease, chronic sinus disease, vocal cord dysfunction, heart disease, or sleep apnoea.

If You Have Asthma, Your Diagnosis Will Include Severity of Your Condition
If you have asthma, your follow-up treatment and long-term prognosis can vary significantly depending on the severity of your condition, its cause, your overall health, and many other variables.

When it comes to the severity of asthma, doctors usually break asthma down into four categories:

Mild intermittent Your asthma symptoms show up less than twice a week, and you wake up on fewer than two nights a month because of your symptoms.
Mild persistent You have symptoms two or more days each week, and you wake up three to four nights a month.
Moderate persistent You have symptoms every day, and you wake up one or more nights a week.
Severe persistent You have symptoms during the day, every day, and you wake up every night due to asthma.
Depending on the severity of your asthma, treatments could range from inhalers to oral or intravenous corticosteroid medication.

It’s important to note that asthma can either be severe because symptoms are persistent all the time (as described above) or because symptoms are difficult to control — either the individual has problems adhering to treatment and symptoms go mismanaged or because symptoms are so severe that even with medication and other treatments, symptoms are difficult to control.

Asthma is a chronic condition, which means it tends never to go away. But with proper care, asthma is manageable and does not lead to early death. “Some patients’ symptoms will become more severe over time, but even in patients with severe asthma, you see some whose symptoms become more mild,” says Emily Pennington, MD, a pulmonologist and asthma specialist at the Cleveland Clinic in Ohio.

Is Diagnosing Asthma in Children Different Than Diagnosing Adults?
In kids age 5 and older, the diagnostic process is more or less the same as the one doctors use to diagnose asthma in adults. But in younger children, a doctor may make a diagnosis based only on symptoms, family history, and a physical exam.

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