Medically reviewed by Farah Khan, MD
Asthma is a chronic lung disease characterized by inflammation and narrowing of the airways, causing symptoms like shortness of breath, wheezing, coughing, and chest tightness. An estimated 226 million people worldwide live with asthma.
Diagnosing asthma typically involves a comprehensive medical evaluation, including a physical examination, medical history review, and diagnostic tests—such as spirometry and other lung function tests—to provide an accurate diagnosis and assess the severity of the condition.
Primary care providers and pediatricians are often the first to diagnose asthma, but allergists (doctors who specialize in allergic conditions) and pulmonologists (doctors who specialize in lung conditions) can also diagnose and manage asthma and other conditions that affect the respiratory system.
If you have asthma symptoms, it is important to see your healthcare provider. Asthma is often a lifelong condition that requires ongoing treatment. The sooner you get diagnosed, the sooner you can begin treatments to help control your symptoms and lower your risk of complications.
Table of Contents
The diagnostic criteria for asthma are based on the assessment of symptoms, medical history, physical exam findings, and lung function tests. The most commonly used criteria for asthma diagnosis are the Global Initiative for Asthma (GINA) criteria, developed by a group of international experts in respiratory medicine, and the National Asthma Education and Prevention Program (NAEPP) guidelines.
The GINA criteria assess four main aspects to establish a diagnosis of asthma:
Symptoms: Typical asthma symptoms, such as coughing, wheezing, shortness of breath, and chest tightness, are experienced and vary over time and in severity.
Documented variation in lung function: People with asthma have variations in lung function, meaning breathing and lung capacity can worsen in response to specific triggers, like exercise. Your doctor may perform lung function tests several times to look for variations in how your lungs work.
Airway hyperresponsiveness: Hyperresponsive airways narrow excessively in response to various triggers, such as exercise or cold air. Bronchial challenge tests measure the sensitivity of your airways during the asthma diagnostic process.
Exclusion of alternative diagnoses: Before diagnosing asthma, your healthcare provider will rule out other conditions that cause similar symptoms, such as heart failure, chronic obstructive pulmonary disease (COPD), or bronchiectasis.
A careful review of your medical history can provide important clues to help your healthcare provider diagnose asthma. When reviewing your medical history, they will consider several key factors to help rule out or diagnose asthma, which may include:
Symptoms: Your provider will ask about your symptoms, including when they started, how often you experience them, and how long they last. They will also ask if anything triggers or worsens your symptoms, such as exposure to exercise, cold air, pollen, or cigarette smoke.
Medical conditions: Tell your doctor about any past or current medical conditions you have. Certain conditions, such as allergic rhinitis or chronic obstructive pulmonary disease (COPD), can increase the risk of asthma or mimic asthma symptoms.
Medication use: Your provider will want to know about your current medications, as some medicines can worsen asthma symptoms, such as beta-blockers or non-steroidal anti-inflammatory drugs (NSAIDs).
Family history: The risk of asthma is higher in people with a family history of asthma or allergies.
Environmental exposures: Your healthcare provider will ask about potential exposure to lung irritants and allergens at home and work.
Your healthcare provider will perform a physical examination to look for signs and symptoms of asthma. During the exam, they will listen to your lungs while you breathe. They will also assess your respiratory rate and look for signs of rapid or shallow breathing. A pulse oximeter may be placed on your finger to measure the oxygen level in your blood.
Lung Function Tests
Lung function tests, or pulmonary function tests, measure different aspects of your respiratory health to confirm or rule out asthma. These tests include spirometry, peak flow meter test, fractional exhaled nitric oxide (FeNO) test, and bronchial provocation Tests.
Spirometry is a non-invasive test that measures how much air you can breathe in and out of your lungs and how quickly. During the test, you will be asked to take a deep breath and exhale forcefully and quickly into a spirometer machine. Spirometry results include:
Your healthcare provider will compare your results to what is considered normal for your age, gender, height, and race. If you have asthma, your FEV1 measurement may be lower than average.
These numbers can be used to calculate your FEV1/FVC ratio. This number represents the percentage of your lung capacity you can exhale in 1 second. For children, your FEV1/FVC ratio is low if it's less than 85%. For adults, the equivalent is less than 70%.
Peak Flow Meter
A peak flow meter is a handheld device that measures the maximum airflow rate you can achieve during a forceful exhale. For a peak flow meter test, you will take a deep breath and forcefully exhale into the peak flow meter. The meter measures how fast you exhale, and your score can determine if your airways are narrowing. These score are separated into three "zones":
Green zone: If you can exhale 80-100% of your usual peak flow rate, your asthma is currently controlled.
Yellow zone: If you can exhale 50-80% of your usual peak flow rate, you are in the cautionary range. It is important to take action and seek appropriate medical attention.
Red zone: If you exhale 50% or less of your usual peak flow rate, you are in the medical alert range. Seek immediate medical attention.
Results can vary depending on each person's technique. For best results, it is recommended regularly test your peak flow so you have a good understanding of your general baseline.
The fractional exhaled nitric oxide (FeNO) test measures the exhaled nitric oxide (NO) level in your breath. NO is a marker of a specific time of airway inflammation.
During the test, you will exhale slowly and steadily into a device measuring how much NO is in your breath. Asthma causes the airways to become inflamed, which increases the amount of NO. High levels of NO indicate airway inflammation—a key feature of asthma. The FeNO test is instrumental in diagnosing eosinophilic asthma, a subtype of asthma characterized by high levels of eosinophils, a type of white blood cell.
Bronchial Provocation Tests
A bronchial provocation test, or methacholine challenge test, determines how reactive or sensitive your airways are.
First, your healthcare provider will ask you to breathe into a spirometer to get a baseline result. Then you will be given a small dose of methacholine, a medicine that narrows the airways. The spirometer test will be repeated to measure how your airways responded to the methacholine. If the methacholine causes a 20% or more reduction in your breathing ability compared to your baseline, the test results will be positive, which indicates that your airways are reactive and you may have asthma.
Allergy testing may be recommended if you experience asthma symptoms after exposure to allergens. Your healthcare provider may recommend allergy testing if they suspect allergies contribute to your asthma symptoms. Common allergy tests include:
Skin prick test: A small amount of a suspected allergen is placed on your skin, which is then scratched to allow the allergen to enter the skin. The skin is examined for signs of an allergy, such as redness, swelling, and/or itching.
Immunoglobulin E (IgE) test: This is a blood test that measures the amount of immunoglobin E (IgE) in the blood. IgE is antibodies the immune system produces in response to an allergen. High levels can indicate an allergy to airborne allergens that can cause or worsen asthma symptoms, such as mold, pet dander, or pollen.
Imaging tests are not often used to diagnose asthma, but healthcare providers may order them to rule out other conditions that can cause asthma-like symptoms or to diagnose asthma in young children who cannot reliably perform lung function tests. These will most likely include a chest X-ray, acid reflux test, or sinus imaging.
Screening for Related Conditions
To make an accurate asthma diagnosis, healthcare providers must rule out other conditions that can cause similar symptoms. Your healthcare provider may order additional imaging tests or diagnostic procedures to rule out the following conditions before diagnosing asthma:
Chronic obstructive pulmonary disease (COPD): COPD is a group of respiratory diseases that share symptoms with asthma, including shortness of breath, coughing, and wheezing.
Bronchiectasis: This is a condition that causes the airways to become damaged and widened, making it difficult to clear mucus from the lungs. It caused symptoms similar to asthma, such as coughing, wheezing, and shortness of breath.
Vocal cord dysfunction (VCD): VCD is a condition in which the vocal cords muscles spasm and constrict the vocal cords from opening properly. VCD can mimic asthma symptoms, such as wheezing and shortness of breath.
Congestive heart failure (CHF): CHF occurs when the heart cannot pump enough blood to meet the body's needs. CHF shares some symptoms with asthma, such as shortness of breath and wheezing, but with CHF, other symptoms are also present, such as swelling in the legs and fatigue.
Gastroesophageal reflux disease (GERD): This is a digestive disorder that occurs when stomach acid flows back into the esophagus, causing irritation and inflammation. GERD can cause symptoms such as chest pain, coughing, and wheezing that can be mistaken for asthma. GERD symptoms are usually worse after eating or when lying down.
In addition to ruling out these conditions, your healthcare provider may screen for comorbid conditions—conditions common in people with asthma. Asthma comorbidities include:
A Quick Review
To diagnose asthma, your healthcare provider will carefully evaluate your symptoms, medical history, and diagnostic test results. Lung function tests, including spirometry and FeNO tests, can help diagnose asthma. Allergy testing, blood tests, and imaging tests may also be used.
Your healthcare provider must rule out other conditions that can mimic asthma symptoms, such as COPD, bronchiectasis, and vocal cord dysfunction. They may screen for comorbid conditions commonly associated with asthma, such as allergies, GERD, and obstructive sleep apnea.
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