A history of coughing, wheezing, and shortness of breath is a good indication of underlying asthma. Since other respiratory conditions may cause these symptoms, your doctor might supplement your history, physical examination, and routine laboratory work with a variety of tests in order to confirm the diagnosis. These may include X rays, special blood tests, skin tests, and pulmonary function tests.
A chest X ray is extremely useful for excluding other chronic lung conditions, such as emphysema, or cystic fibrosis in children. It also serves as a baseline test against which future improvements may be measured.
RAST is a very sophisticated blood test that determines the level of IgE antibodies you possess to particular allergens. The main advantage of this test is that a small sample of blood may be used to test for many different allergens. The disadvantage is that the test has a lower success rate than the routine skin tests for allergens briefly described below. For this reason doctors would say that the RAST is less sensitive than skin testing, and owing to this, some skin testing is often necessary to supplement the RAST.
Skin tests are an important part of an asthma workup. They are not only useful for indicating what substances you are allergic to but the severity of your allergies as well. Scratch tests and puncture tests involve making a series of tiny scratches or punctures in the skin and then applying extracts of potential allergens; a positive result is the development of redness, swelling, or hives at the test sites. Intradermal tests, which are performed in the same fashion as the familiar PPD screening test for tuberculosis, are similar to scratch tests except that the material is injected superficially under the skin; again, redness, swelling, or hives suggests an allergy to the test substance.
Spirometry, or pulmonary function studies, may also be ordered to evaluate breathing function. Performed in the office, this testing essentially involves inhaling and exhaling through a tube that is attached to a recording machine which is capable of registering and graphing your level of respiratory function. The test measures not only how much air you are able to move in and out of your lungs but how quickly you can do it, both before and after the use of bronchodilator medications (see below). A marked improvement in your breathing function after the use of bronchodilators is a good indication of the presence of asthma, which by definition is largely a reversible airway problem. Spirometry is also useful, once a diagnosis has been confirmed, for evaluating the effectiveness of treatment.
Another instrument, the peak flow meter, is a small plastic device used by the patient at home to measure the rate of airflow out of the lungs. The test itself is quite simple to perform. The individual first inhales as deeply as possible and then blows out into the machine as rapidly as possible. Two readings are generally taken each day, once shortly after arising and then again later in the day. Since lung function in asthmatics is generally worse in the morning and improves as the day progresses, a decrease between the morning and afternoon readings signals a problem. In addition, comparing daily recordings is useful for assessing overall progress. These devices are mostly recommended for severe asthmatics who must keep a close watch on their respiratory status and response to medications.
