How Asthma Is Diagnosed

Asthma is diagnosed based on your symptoms, a physical exam, and various tests, including lung function tests to evaluate breathing. Because the telltale symptoms of asthma are common in other respiratory conditions, differential diagnosis also may be necessary to rule out causes other than asthma.

This article will discuss the various types of tests that may be part of a diagnostic workup for asthma.

Self Checks / At-Home Testing

Asthma is not a disease that can be self-diagnosed. But becoming familiar with the most common symptoms can alert you to the possibility you or your loved one might have asthma, in particular:

• Wheezing
• Shortness of breath (dyspnea)
• Chest tightness
• Cough

If you develop these symptoms and they become persistent, make an appointment to see your healthcare provider or a pulmonologist (a physician who specializes in respiratory diseases).

Physical Examination

To diagnose asthma, your healthcare provider will start by asking about your medical history and ongoing health issues. Asthma is especially common in people who have atopic conditions such as hay fever (allergic rhinitis) or atopic dermatitis.

They will want as many details about your symptoms as you can provide. This is why keeping a record of your symptoms is invaluable. Also, share with the healthcare provider any changes you've made in your daily life that might have been prompted by asthma symptoms.

The next step in diagnosing asthma will likely be a physical exam that focuses on your breathing. The healthcare provider will listen carefully for wheezing, which isn't present all the time in people with asthma, but if it happens to occur during your appointment it will provide a strong clue as to your diagnosis.

Lung Function Tests

If your healthcare provider finds signs of asthma, they will likely run a lung function test to get more information about the type and severity of your condition.

Spirometry

Spirometry is the most common lung function test. To do this test, you put a mouthpiece in your mouth and a clip on your nose. You then breathe into a tube connected to a small device called a spirometer.

This device measures two things:

• Forced expiratory volume in one second (FEV1): How much air you can blow out in one second.
• Forced vital capacity (FVC): How much air you can blow out in one breath.

If your results show reduced lung function, your technician may give you a medicine called a bronchodilator to open your airways. You'll then take the test again to see if your lung function improves. If the medication brings about an increase in airflow of 12%, it is an indication that asthma is the cause of symptoms.

Peak Expiratory Flow Meter Test

Peak expiratory flow rate (PEFR) is a measurement of how powerfully you can blow air out of your lungs. This is measured with a simple hand-held device called a peak flow meter. A normal PEFR is 80% or greater than what would be predicted for the person being tested.

Fractional Exhaled Nitric Oxide (FeNO) Test

If after routine testing, an asthma diagnosis isn't certain, a fractional exhaled nitric oxide test may be performed. This test is often simply referred to as a FeNO test.

A FeNO test uses a handheld device to measure the amount of nitric oxide you exhale. Having a high level of nitric oxide in your exhaled breath often means your airways are inflamed (swollen).

Provocation Tests

If your doctor wants to see how sensitive your lungs are, they may have you do a provocation test. These tests are also called bronchoprovocation challenges or tests.

You'll take a breathing test (spirometry) before and after each challenge. This allows your healthcare provider to see if your lung function changes and if so, by how much. The most common provocation tests are:

• Exercise challenges: During an exercise challenge, you'll be asked to walk or jog on a treadmill. A technician will measure your lung function during an exercise test before, during, and after exercise. If your breathing ability decreases by 10% or more after exercising, you likely have exercise-induced bronchoconstriction (EIB).
• Irritant challenges: During an irritant test, a technician exposes you to an asthma trigger to see if your airways react. Potential triggers include perfume or smoke.
• Methacholine challenge: During this test, you'll breathe in increasing doses of an inhaled drug called methacholine. If your lung function drops by 20% or more from the baseline, you may have asthma. This test is used when suspicion is high, but spirometry is ambiguous or normal.

If your airways tighten during any of these tests, you'll be given a fast-acting bronchodilator to re-open them. 

Imaging Tests

Most people with asthma have normal chest X-rays, but some healthcare providers order them for patients who are experiencing wheezing for the first time. This is because if asthma has gone undiagnosed for a long time, a chest X-ray may reveal hyperinflation (overinflated lungs).

Differential Diagnoses

Because wheezing can be symptomatic of diseases other than asthma, your healthcare provider may need to rule them out to definitively diagnose asthma:

• Gastroesophageal reflux disease (GERD): GERD may lead to wheezing and cough; it's also commonly responsible for nighttime symptoms. Patients commonly experience a painful burning sensation as well as a sour or bitter taste in the back of the mouth.
• Congestive heart failure: This is a condition where the heart's pump is failing and unable to provide adequate blood supply. In addition to asthma-like symptoms, there may be swelling in both legs and difficulty breathing while lying down.
• Chronic obstructive pulmonary disease (COPD): A significant difference between COPD and asthma is that COPD often is characterized by a morning cough, while asthma symptoms can occur at any time and often only after exposure to triggers.
• Pulmonary embolism (PE): The sudden onset of shortness of breath and chest pain is the most common symptom of PE, but the condition sometimes causes wheezing that could initially be mistaken for asthma.
• Cystic fibrosis (CF): CF patients will wheeze, as well as experience shortness of breath and cough. However, this chronic illness is also associated with poor growth and several other problems in early childhood.

Summary

If you have persistent symptoms of wheezing, coughing, shortness of breath, and chest tightness, you should see a healthcare provider to get checked out. They will likely take your medical history, do a physical exam, and give you a series of breathing tests to see how well air can move in and out of your lungs. This is usually enough to diagnose asthma, but in some cases, imaging tests such as an X-ray might be done as well.

A Word From Verywell

Because asthma is a progressive disease—one that can worsen without treatment—it's imperative to see a healthcare provider as soon as symptoms arise. An early diagnosis is key to effective treatment and preventing the disease from interfering with your quality of life.