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To diagnose asthma, your doctor will review your medical history, family history, and symptoms, looking for breathing problems, asthma in other family members, allergies, eczema, or other lung conditions. It is important that you describe symptoms such as coughing, wheezing, shortness of breath, or chest tightness in detail, 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 may perform, including pulmonary function tests, allergy tests, blood tests, and chest and sinus X-rays. These tests help your doctor determine if asthma is present and if other conditions affect it. Two medical conditions that may make asthma harder to treat and control are sinusitis and gastroesophageal reflux disease, commonly called GERD. If you are diagnosed with asthma, your doctor may also test you for these conditions so that they can be treated.

Sinusitis, also called sinus infection, is an inflammation of the sinuses. When the sinuses become blocked and filled with fluid, bacteria grow, causing infection and inflammation. Your doctor may order a special sinus X-ray, called a CT scan, to evaluate your sinuses if he suspects an infection. Once acute sinusitis is diagnosed, you will be treated with antibiotics for at least 10 to 12 days.

This section includes more on pulmonary function tests.

Pulmonary function tests

The two most common lung-function tests used to diagnose asthma are spirometry and methacholine challenge tests.

  • Spirometry: This simple breathing test measures how much air you can blow out of your lungs and how fast. 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. The bronchodilator causes your airways to expand, allowing for air to pass through freely. The test is also used to monitor patient progress and help doctors determine if and how to adjust a treatment plan.
  • Methacholine challenge test: This test is more commonly used for adults than for children. It may 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. Before taking a methacholine challenge test, be sure to tell your doctor if you have recently had a viral infection or any shots or immunizations, since these may affect the test's results.

Here are other general preparations to make before the methacholine test:

  • No smoking on the day of the test
  • No caffeine (coffee, tea, cola, or chocolate) for 24 hours before the test
  • Avoid exercise and cold-air exposure on the day of test.
  • Medications taken to treat asthma can affect the test results. Your doctor will tell you how long before testing you should discontinue any medications you are taking.

Last reviewed on 8/26/08

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