Introduction: Who Should Be Tested and When

If you or someone you love has asthma, understanding when to seek diagnostic testing is essential. Asthma is a chronic lung condition where the airways become inflamed, narrow, and produce extra mucus, making breathing difficult. An asthmatic crisis, also called an asthma attack or exacerbation, happens when symptoms suddenly worsen and standard medications stop working as they should.^[1][3]

Not everyone with asthma will experience a crisis, but when one occurs, it can be frightening and even life-threatening. Symptoms may develop over hours or days, or they can come on quickly within minutes. During an attack, the sides of your airways swell, the muscles around them tighten, and thick mucus clogs the passages, making it extremely hard to breathe.^[2][5]

You should seek diagnostic evaluation if you notice symptoms like frequent coughing (especially at night), wheezing when you breathe out, shortness of breath, chest tightness, or trouble sleeping due to breathing problems. These signs suggest that asthma might not be under control, or that you are experiencing an exacerbation.^[1][2]

Children may show slightly different warning signs. Parents should watch for increased coughing, decreased exercise tolerance, difficulty with daily activities, or sudden worsening of wheezing or shortness of breath. Common triggers for children include colds, exposure to smoke, allergens like pet dander or pollen, strong smells, weather changes, running or playing hard, and even crying or laughing.^[9][14]

Adults should be especially alert if they need to use their quick-relief inhaler more often than usual, if symptoms prevent normal activities, or if they wake up at night struggling to breathe. A severe asthma attack is a medical emergency. If you experience obvious difficulty breathing, cannot speak a full sentence in one breath, notice skin tugging between your ribs or at the base of your neck, feel dizziness or confusion, or see bluish fingers, lips, or skin, call emergency services immediately.^[3][7][17]

Diagnostic Methods for Identifying Asthma and Asthmatic Crisis

Diagnosing asthma and determining the severity of an asthmatic crisis involves a combination of medical history, physical examination, and specialized tests. Your doctor will start by asking detailed questions about your symptoms, how often they occur, what seems to trigger them, and whether anyone in your family has asthma, allergies, or breathing problems. This conversation helps the doctor understand your condition and rule out other illnesses that might cause similar symptoms.^[7][11]

During the physical exam, your doctor will listen to your chest with a stethoscope to detect wheezing, check how fast you are breathing, and look for signs of respiratory distress such as use of accessory muscles (muscles in your neck or chest working harder than usual to help you breathe). They may also check your oxygen levels and overall appearance to assess how severe the situation is.^[5][10]

Lung Function Tests

The most important tools for diagnosing asthma are lung function tests. These measure how well air moves in and out of your lungs and how much air you can exhale. The results help doctors determine whether your airways are narrowed and how much.^[11]

Spirometry is the main test used. During spirometry, you take a deep breath and then blow out as hard and fast as you can into a machine. The machine measures the amount of air you exhale and how quickly you can do it. This measurement is called forced expiratory volume (FEV-1). Your result is compared to what is expected for someone of your age, height, and sex who does not have asthma. If your airways are narrowed, your FEV-1 will be lower than normal. Often, the test is repeated after you inhale a medication called a bronchodilator, which opens the airways. If your lung function improves after using the bronchodilator, this strongly suggests asthma.^[10][11]

Another simple tool is the peak flow meter, a handheld device you can use at home. It measures how fast you can blow air out of your lungs, called peak expiratory flow (PEF). Your doctor may ask you to track your peak flow readings over several weeks. Lower-than-usual readings can warn you of an asthma attack even before you notice symptoms. Peak flow readings are usually given as a percentage of your personal best—the highest number you can achieve when your asthma is well controlled.^[10][11]

Additional Diagnostic Tests

In some cases, doctors use additional tests to confirm asthma or understand what triggers your symptoms. A methacholine challenge test involves inhaling a substance called methacholine, which is known to trigger airway narrowing in people with asthma. If your airways react and narrow after inhaling methacholine, it is likely you have asthma. This test is sometimes used even if your initial spirometry results are normal.^[11]

Allergy testing can identify whether you are allergic to pets, dust, mold, pollen, or other common triggers. Allergies often play a role in asthma, especially in children. Allergy tests can be done with a skin prick test or a blood test. Knowing your specific allergens helps you and your doctor develop a plan to avoid triggers.^[2][11]

A chest X-ray may be ordered to rule out other conditions that cause breathing problems, such as infections or structural abnormalities in your lungs or heart. Similarly, imaging tests like a chest CT scan can provide more detailed pictures if needed.^[11]

Pulse oximetry is a simple, painless test where a small clip is placed on your fingertip. It measures the amount of oxygen in your blood. Low oxygen levels can indicate that your lungs are not delivering enough oxygen to your body, which is a sign of a severe asthma attack.^[10]

During an asthma attack, doctors may also measure arterial blood gases (ABG), which involves taking a small blood sample from an artery, usually in your wrist. This test shows how much oxygen and carbon dioxide are in your blood. High levels of carbon dioxide or low levels of oxygen are warning signs of a serious, life-threatening attack.^[5]

A newer test called exhaled nitric oxide (FeNO) measurement checks the amount of nitric oxide gas in your breath when you exhale. High levels of nitric oxide suggest inflammation in your lungs, which is common in asthma. This test is not usually done during an emergency, but it can help guide long-term treatment.^[10]

Blood tests may also be performed. Doctors can check for eosinophils, a type of white blood cell that increases when there is inflammation, especially in allergic or eosinophilic asthma. High eosinophil counts can help identify the type of asthma you have and guide treatment choices.^[2]

Assessing Severity During a Crisis

When you arrive at a clinic or emergency department during an asthmatic crisis, the goal is to assess how severe your attack is and start treatment immediately. Doctors classify asthma exacerbations as mild, moderate, severe, or life-threatening based on your symptoms, physical exam findings, lung function measurements, and oxygen levels.^[16][18]

Mild to moderate attacks may involve some difficulty breathing, the ability to speak in full sentences, and a peak flow reading between 50 and 79 percent of your personal best. Severe attacks mean obvious difficulty breathing, inability to speak full sentences, fast heart rate, and peak flow below 50 percent of your best. Life-threatening attacks involve extreme difficulty breathing, confusion, bluish skin, and dangerously low oxygen levels.^[3][17]

Tests and treatments often happen at the same time in an emergency. Your healthcare team will monitor your response to medications, recheck your lung function, and adjust treatments as needed to stabilize your breathing and prevent complications.^[10]

Diagnostics for Clinical Trial Qualification

If you are interested in participating in a clinical trial for asthma, you will likely undergo additional diagnostic tests beyond those used in routine care. Clinical trials are research studies that test new treatments or better ways to manage asthma. To join a trial, you must meet specific criteria, and doctors use standardized tests to make sure participants fit the study’s requirements.^[12]

Clinical trials for asthma typically require detailed documentation of your asthma diagnosis, including confirmed airway obstruction or hyperresponsiveness. This means you will need to have spirometry results showing reduced lung function or a positive methacholine challenge test. Trials may also require proof that your asthma symptoms respond to bronchodilators, which is demonstrated by improvement in FEV-1 after inhaling a quick-relief medication.^[11]

Researchers often look for participants with specific types or severities of asthma. For example, some trials focus on people with severe asthma whose symptoms are not controlled despite using high-dose inhaled medications. Others may target eosinophilic asthma, where high levels of eosinophils in the blood or sputum drive inflammation. If you have this type, you may need a blood test to measure your eosinophil count or a sputum test where you cough up mucus for analysis.^[2]

Some trials require measurement of biomarkers, which are substances in your body that indicate disease activity. For asthma, this might include testing exhaled nitric oxide levels or measuring a protein called periostin in your blood. These markers help researchers understand how inflammation affects your lungs and whether a new treatment might work for you.^[10]

Allergy testing is also common in clinical trial screening. If a trial is testing a treatment for allergic asthma, you may need skin prick tests or blood tests (measuring immunoglobulin E, or IgE, which is an antibody involved in allergic reactions) to confirm that allergens trigger your asthma.^[2][11]

Clinical trials may also require chest X-rays or CT scans to ensure there are no other lung diseases or structural problems that could interfere with the study. Similarly, you may have an electrocardiogram (ECG) to check your heart function, especially if the trial involves medications that could affect the heart.^[11]

Peak flow monitoring and asthma control questionnaires are often used throughout a trial to track how well treatments are working. You may be asked to record your symptoms daily, measure your peak flow at home, and report how often you need to use your rescue inhaler. These records help researchers see if the new treatment improves your asthma control over time.^[12]

Participating in a clinical trial gives you access to new treatments and close medical monitoring, but it also requires commitment. You will have more frequent clinic visits, additional tests, and strict requirements for taking medications as directed. Before enrolling, the research team will explain all the tests and procedures, answer your questions, and make sure you understand what participation involves.^[12]