Step 4: How asthma is diagnosed
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To diagnose asthma, the doctor will see if three criteria are met:

  1. You have recurring episodes where your airflow becomes blocked, resulting in at least one of the asthma signs
  2. The blocked airflow can be at least partially reversed through medication (see spirometry, below)
  3. Other potential causes of your symptoms are ruled out

Medical history

The doctor will want to evaluate your medical history to identify what symptoms you have had, when your symptoms occur, and how long they last. The doctor will ask about possible triggers, such as allergens, exercise, or occupational exposure to chemicals. The doctor will also want to know if you have a family history of asthma, allergy, sinusitis, or nasal polyps.

Physical exam

The doctor will conduct a physical exam that focuses on the upper respiratory tract, chest, and skin. The doctor will listen for wheezing and may look for nasal secretions, eczema, and similar allergy-related symptoms.

Lung function tests

Spirometry is the most reliable test for diagnosing asthma. A spirometer is an instrument that measures the maximum volume you can exhale after breathing in as much as you can. The total volume you exhale is called "forced vital capacity," or FVC. The spirometer also measures the volume of air you exhale in the first second. (This is referred to as "forced expiratory volume in one second," or FEV1.) In general, the more air you breathe out during the first second of a full exhalation, the better.

The doctor will take the reading several times. Your FVC and FEV1 results will be compared to what is normally seen in people without any blockage in their airways. Your doctor will have a good idea just from this data how much "obstruction" is in your airways.

Then, you will be given a bronchodilator, a drug that relaxes the muscles of your airways. After the drug has had time to take effect, you blow into the spirometer again. If you can breathe out significantly more air during the first second than you could before, it indicates that your breathing obstruction is "reversible." This is a strong indication of asthma.

Many doctors use a "peak flow meter" to diagnose asthma. This simple, portable device is available in most doctor's offices and may allow a doctor to quickly and easily determine whether asthma is your problem.

Because both spirometry and peak flow measurements require coordinated cooperation from the person being tested, they may not be practical in children younger than 6. (About 80% of all asthma begins before age 6). In younger children, lung function can be measured by a technique called forced oscillation, which simply involves breathing vibrating air. Often the diagnosis is based on the medical history and physical exam, perhaps with some other supporting tests.

Other tests

No one single test, or set of tests, is appropriate for every patient. Your doctor may use other tests, such as chest x-rays, to help rule out the possibility of other causes of your symptoms. The doctor may perform additional lung function tests to rule out bronchitis or emphysema (especially if you are a smoker or an older patient).

A test called "bronchoprovocation" may be performed if the doctor strongly suspects asthma but your spirometry readings were normal. (This test must be conducted by a trained specialist in an appropriate facility.) Other tests include chest x-rays, allergy testing, examinations for nasal polyps or sinusitis, and evaluation for gastroesophageal reflux.

Allergy testing can provide important supportive evidence [the Childhood Asthma Management Program (CAMP) reports that about 88% of school-aged children with asthma have positive allergy prick skin tests to inhaled allergens]. Not only can allergy testing support the diagnosis, but treating the allergies can help manage the asthma. Allergy test results can help predict the long-term course of child asthma.

Throat Clearing - An Important Clue?

Might throat-clearing be an overlooked symptom of asthma? Researchers surveyed the parents of over 2,500 3- to 5-year-old children attending daycare on the island of Crete. Among the questions asked: "Does your child have a habit of clearing his or her throat often?" More than 100 parents said yes. Many of those children already had been diagnosed with asthma, but most had not.

When pulmonary function testing was performed on the children believed not to have asthma, the results were enlightening: These children all had mild asthma that had not yet been suspected! And their lung function and throat clearing improved with asthma medicines. The study, published in the April 10, 2003, issue of the New England Journal of Medicine, suggests that throat clearing may be the first sign of asthma in some children. Children with asthma fare better with early diagnosis and early treatment. It might be wise for doctors thinking about asthma to ask parents about throat clearing, and for parents whose children often clear the throat to ask their doctors about asthma testing.

If it is asthma...

If you or your child has asthma or recurrent wheezing, ask your doctor what category of asthma it is. Those with mild intermittent asthma might be managed with occasional albuterol use. Those with mild persistent asthma (or moderate or severe persistent asthma) fare much better if they also receive anti-inflammatory or preventive medicines. One study, though, found that most children with persistent asthma are assumed by doctors and parents to have intermittent asthma. Thus, they miss out on getting the right medicines -- medicines that could actually improve their asthma and result in less albuterol being needed. Classifying your asthma is a conversation you want to have!

If it's not asthma...

According to the National Institutes of Health, "recurring episodes of cough and wheezing are almost always due to asthma in both children and adults." However, there are other possibilities. A certain amount of airway inflammation and narrowing are NORMAL responses to airborne irritants. Recurrent wheezing could come from ongoing exposure to chemical fumes, for example. It's only asthma if the narrowing is out of proportion to the threat to the lungs. And in young adults, "vocal cord dysfunction" can cause symptoms very similar to asthma, such as shortness of breath and wheezing.

Regardless of age, if asthma is ruled out, your doctor will explain other potential causes.


National Asthma Education and Prevention Program Expert Panel Report: guidelines for the diagnosis and management of asthma update on selected topics -- 2002. J Allergy Clin Immunol. 2002 Nov;110(5 pt 2):S141-219.

National Asthma Education and Prevention Program Expert Panel Report 2: guidelines for the diagnosis and management of asthma. Bethesda (MD): U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, National Heart, Lung and Blood Institute; 1997 Jul. NIH Publications 97-4051.

Williams SG, Schmidt DK, Redd SC, Storms W. Key clinical activities for quality asthma care: recommendations of the National Asthma Education and Prevention Program. MMWR Recomm Rep. 2003 Mar 28;52(RR-6):1-8.


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Review Date: 5/16/2007

Reviewed By: Alan Greene, M.D., F.A.A.P., Department of Pediatrics, Packard Children's Hospital, Stanford University School of Medicine; Chief Medical Officer, A.D.A.M., Inc.

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