Diagnosing asthma involves a thorough medical history, physical exam and lung function tests
If you have wheezing, coughing and shortness of breath, your doctor may suspect you have asthma. But these signs and symptoms alone aren’t enough to diagnose asthma because they can also be caused by other conditions. Your doctor will base your diagnosis on a number of things, including a physical exam and answers to questions about your symptoms and health (medical history). In addition, you may need further evaluation, which can include lung function tests or other tests.
Medical history
Your doctor will ask you about several things, which may include:
■What your symptoms are
■If you have hay fever or other allergies — which can be linked to asthma
■Whether you have any biological (blood) relatives with hay fever or other allergies
■What health problems you have now or have had in the past
■What medications or herbal supplements you take
Physical exam
A physical exam for possible asthma generally includes:
■An examination of your nose, throat and upper airways (upper respiratory tract).
■Listening to the sounds your lungs make with a stethoscope as you breathe. Wheezing — high-pitched whistling sounds when you breathe out — is one of the main signs of asthma.
■Examining your skin for signs of allergic conditions such as eczema and hives, which are often associated with asthma.
Lung function tests
Spirometer
Although your symptoms, medical history and physical examination may suggest that you have asthma, lung function tests (also called pulmonary function tests) may be needed to confirm an asthma diagnosis. Lung function tests may include one or more of the following tests.
Spirometry
This noninvasive test measures how well you breathe. During spirometry, you take deep breaths and forcefully exhale into a hose connected to a machine called a spirometer. Spirometry testing reveals two measurements that are important in diagnosing asthma:
■Forced vital capacity (FVC), which is the maximum amount of air you can inhale and exhale
■Forced expiratory volume (FEV-1), which is the maximum amount of air you can exhale in one second
Your doctor will compare these two measurements. If certain key measurements are below normal for a person your age, it may be a sign that your airways are obstructed. Your doctor may ask you to inhale a bronchodilator drug used in asthma treatment to open obstructed air passages and then try the test again. If your measurements improve significantly, it’s likely that you have asthma. Your doctor may still suspect that you have asthma even if your initial spirometry measurements are normal. If so, you may need additional tests.
Exhaled nitric oxide test
A relatively new tool for measuring asthma, the nitric oxide test is available in only some hospitals and doctors’ offices. High levels of nitric oxide gas in the air you breathe out can be a sign of asthma. Nitric oxide gas is produced by the body normally, but high levels in your breath can mean your airways are inflamed — a sign of asthma.
Challenge test
During this test, your doctor deliberately tries to trigger airway obstruction and asthma symptoms by having you inhale an airway-constricting substance such as methacholine. If you appear to have asthma triggered by exercise (exercise-induced asthma), you may be asked to do vigorous physical activity to trigger symptoms.
After triggering your symptoms, you retake the spirometry test. If your spirometry measurements are still normal, it’s likely that you don’t have asthma. But if your measurements have fallen significantly, it may mean you have asthma.
When checking children under age 5, doctors seldom conduct lung function tests because young children usually have trouble following the instructions. Instead, when a child’s signs and symptoms, medical history, and physical examination suggest asthma, the doctor may prescribe a bronchodilator — a drug that opens the airways. If your child’s signs and symptoms improve after using the bronchodilator, an asthma diagnosis is likely.
Additional tests: Ruling out conditions other than asthma
Depending on your age, your medical history and initial testing, your doctor may suspect that you have a condition other than asthma. Conditions that can cause asthma-like symptoms include:
■Other lung disease such as chronic obstructive pulmonary disease (COPD)
■Airway tumors
■Airway obstruction
■Bronchitis
■Lung infection (pneumonia)
■Blood clot in the lung (pulmonary embolism)
■Congestive heart failure
■Vocal cord dysfunction
■Viral lower respiratory tract infection
If your doctor suspects that you have another condition, you may have other tests, such as:
■Chest and sinus X-rays
■Complete blood count
■Computerized tomography (CT) scans of the lungs
■Gastroesophageal reflux assessment
■Sputum induction and examination
Your doctor may also want to see whether you have any other conditions that can accompany asthma. These include:
■Heartburn, or gastroesophageal reflux disease (GERD)
■Hay fever
■Sinusitis
Your doctor may also perform allergy tests. Although allergy tests aren’t used to diagnose asthma, they can help identify substances that may be causing or worsening your asthma.
“Asthma Diagnosis”
When asthma is suspected, the patient should describe for the doctor any pattern related to the symptoms and possible precipitating factors, including:
•Whether symptoms are more frequent during the spring or fall (allergy seasons).
•Whether exercise, a respiratory infection, or exposure to cold air has ever triggered an attack.
•Any family history of asthma or allergic disorders, such as eczema, hives, or hay fever.
•Any occupational or long-term exposure to chemicals. Early detection of occupational asthma is very important. If symptoms improve on weekends and vacation and are worse at work, the job is likely to be the source of the asthma, although this is not always the case. Asthma is common, and exacerbation at work may be coincidental.
Ruling Out Other Diseases
A number of disorders may cause some or all of the symptoms of asthma:
•Asthma and chronic obstructive lung diseases (chronic bronchitis and emphysema) affect the lungs in similar ways and, in fact, may all be present in the same person. Unlike other chronic lung conditions, asthma usually first appears in patients less than 30 years old and with chest x-rays that are normal. Still, it may be difficult to distinguish these disorders in some adults with late onset asthma.
•Panic disorder can coincide with asthma or be confused with it.
•Gastroesophageal reflux disorder (GERD) is a common companion in asthma and may affect treatment.
•Other diseases that must be considered during diagnosis are pneumonia, bronchitis, severe allergic reactions, pulmonary embolism, cancer, heart failure, tumors, psychosomatic illnesses, and certain rare disorders (such as tapeworm and trichomoniasis).
Pulmonary Function Tests
If symptoms and a patient’s history suggest asthma, the doctor will usually perform tests known as pulmonary function tests to confirm the diagnosis and determine the severity of the disease.
Using a spirometer, an instrument that measures the air taken into and exhaled from the lungs, the doctor will determine several values:
1. Vital capacity (VC), which is the maximum volume of air that can be inhaled or exhaled.
2. Peak expiratory flow rate (PEFR), commonly called the peak flow rate, which is the maximum flow rate that can be generated during a forced exhalation.
3. Forced expiratory volume (FEV1), which is the maximum volume of air expired in one second.
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How Is Asthma Diagnosed?
Your primary care doctor will diagnose asthma based on your medical history, a physical exam, and results from tests. He or she also will figure out what your level of asthma severity is—that is, whether it’s intermittent, mild, moderate, or severe. Your severity level will determine what treatment you will start on.
You may need to see an asthma specialist if:
You need special tests to be sure you have asthma
You’ve had a life-threatening asthma attack
You need more than one kind of medicine or higher doses of medicine to control your asthma, or if you have overall difficulty getting your asthma well controlled
You’re thinking about getting allergy treatments
Medical History
Your doctor may ask about your family history of asthma and allergies. He or she also may ask whether you have asthma symptoms, and when and how often they occur. Let your doctor know if your symptoms seem to happen only during certain times of the year or in certain places, or if they get worse at night.
Your doctor also may want to know what factors seem to set off your symptoms or worsen them.
Your doctor may ask you about related health conditions that can interfere with asthma management. These conditions include a runny nose, sinus infections, reflux disease, psychological stress, and sleep apnea.
Physical Exam
Your doctor will listen to your breathing and look for signs of asthma or allergies. These signs include wheezing, a runny nose or swollen nasal passages, and allergic skin conditions such as eczema.
Keep in mind that you can still have asthma even if you don’t have these signs on the day that your doctor examines you.
Diagnostic Tests
Lung Function Test
Your doctor will use a test called spirometry (spi-ROM-eh-tre) to check how your lungs are working. This test measures how much air you can breathe in and out. It also measures how fast you can blow air out. Your doctor also may give you medicines and then test you again to see whether the results have improved.
If the starting results are lower than normal and improve with the medicine, and if your medical history shows a pattern of asthma symptoms, your diagnosis will likely be asthma.
Other Tests
Your doctor may order other tests if he or she needs more information to make a diagnosis. Other tests may include:
Allergy testing to find out which allergens affect you, if any.
A test to measure how sensitive your airways are. This is called a bronchoprovocation test. Using spirometry, this test repeatedly measures your lung function during physical activity or after you receive increasing doses of cold air or a special chemical to breathe in.
A test to show whether you have another disease with the same symptoms as asthma, such as reflux disease, vocal cord dysfunction, or sleep apnea.
A chest x ray or an EKG (electrocardiogram). These tests will help find out whether a foreign object or other disease may be causing your symptoms.
Diagnosing Asthma in Young Children
Most children who have asthma develop their first symptoms before 5 years of age. However, asthma in young children (aged 0 to 5 years) can be hard to diagnose. Sometimes it can be difficult to tell whether a child has asthma or another childhood condition because the symptoms of both conditions can be similar.
Also, many young children who have wheezing episodes when they get colds or respiratory infections don’t go on to have asthma after they’re 6 years old. These symptoms may be due to the fact that infants have smaller airways that can narrow even further when they get a cold or respiratory infection. The airways grow as a child grows older, so wheezing no longer occurs when the child gets a cold.
A young child who has frequent wheezing with colds or respiratory infections is more likely to have asthma if:
One or both parents have asthma
The child has signs of allergies, including the allergic skin condition eczema
The child has allergic reactions to pollens or other airborne allergens
The child wheezes even when he or she doesn’t have a cold or other infection
A lung function test along with a medical history and physical exam is the most certain way to diagnose asthma. However, this test is hard to do in children younger than 5 years. Thus, doctors must rely on children’s medical histories, signs and symptoms, and physical exams to make a diagnosis. Doctors also may use a 4 to 6 week trial of asthma medicines to see how well a child responds.