To diagnose asthma, your doctor will review your medical history, family
history, and symptoms. He or she will be interested in any history of breathing
problems you might have had, as well as a family history of asthma or other lung
conditions, allergies, or a skin disease called eczema. It is important that you
describe your symptoms in detail (coughing, wheezing, shortness of breath, chest
tightness), including when and how often they occur.
Your doctor will also perform a physical examination and listen to your heart
and lungs.
There are many tests your doctor might perform, including pulmonary function
tests, allergy tests, blood tests, and chest and sinus X-rays. All of these
tests help your doctor determine if asthma is indeed present and if there are
other conditions affecting it.
What are pulmonary function tests?
Pulmonary function tests (or lung function tests) include numerous
procedures to diagnose lung problems. The two most common lung function tests
used to diagnose asthma are spirometry and methacholine challenge tests.
Spirometry — This is a simple breathing test that measures how much
and how fast you can blow air out of your lungs. It is often used to determine
the amount of airway obstruction you have. Spirometry can be done before and
after you inhale a short-acting medication called a bronchodilator, such as
albuterol. The bronchodilator causes your airways to expand, allowing
for air to pass through freely. This test might also be done at future doctor
visits to monitor your progress and help your doctor determine if and how to
adjust your treatment plan.
Methacholine challenge test — This test is more commonly
used in adults than children. It might be performed if your symptoms and screening spirometry do not clearly or convincingly establish a diagnosis of asthma. Methacholine is an agent that, when inhaled, causes the airways to spasm and narrow if asthma is present. During this test, you inhale increasing amounts of methacholine aerosol mist before and after spirometry. The methacholine test is
considered positive — meaning asthma is present — if the lung function drops by at
least 20 percent. A bronchodilator is always administered at the end of the test to
reverse the effects of the methacholine.
How do I prepare for pulmonary function tests?
Ask your doctor if there is anything you need to do to prepare for
spirometry.
Before taking a methacholine challenge test, be sure to tell your doctor if
you have recently had a viral infection, like a cold, or any shots or
immunizations, since these might affect the test's results.