Asthma Medicines

Following the careful review of the patient’s history and physical examination the physician will proceed to several commonly used laboratory tests to complete the diagnostic evaluation. There is no universal”checklist” of tests for every patient since there is great variation in each case. Physicians may also have differences in their laboratory evaluations.

Blood Tests

In the laboratory evaluation of asthma it would be common to evaluate the patient’s blood count looking for “allergy cells” called eosinophils. The physician may also obtain a level of IgE, the immunoglobulin in the blood that is often elevated in allergic patients. .

X-rays

A chest x-ray is often necessary to exclude many of the entities discussed above that can mimic asthma. It does not serve to confirm the diagnosis since the features of asthma occurring within the bronchial tubes cannot be seen on a chest x-ray.

Occasionally, the chest x-ray may show that the lungs are greatly expanded and appear larger than normal or hyperinflated. This occurs in asthma because air may enter the bronchial tubes but have difficulty being exhaled, also known as “air-trapping.” This x-ray finding cannot be used as a diagnostic tool for asthma since the same finding may occur in emphysema and in some cases of bronchitis.

Often the physician will order sinus x-rays as part of the laboratory evaluation. Evidence of sinusitis or nasal polyps would identify patients as high-risk candidates for asthma. In addition, the sinusitis may be viewed as a potential aggravating factor in asthmatic attacks and thus become a focus of treatment of individual patients. There is a recent trend toward using the more detailed CAT scan for this exam because of the increased information it provides.

Sputum Exam

Examination of swabs of nasal mucus or chest phlegm (sputum) may be helpful in diagnosing asthma. Microscopic examination may identify abundant eosinophils that would be characteristic of allergy and asthma. The presence of pus cells called neutrophils would suggest an infectious process; for example, bronchitis or sinusitis. The physician may request a culture of the coughed sputum if pus cells are seen under the microscope.

Pulmonary Function Testing

Forced Expiratory Maneuver

The most important laboratory test the physician performs in the diagnosis of asthma is pulmonary function testing. Before the testing begins the patient’s age, race, sex, height, and weight are recorded. From these statistics the expected normal values are determined. These are called the predicted normals and they are determined from statistical analysis of large groups of normal subjects.

The most common test involves a device known as a spirometer, which measures the amount of air (volume) expelled by the patient as well as its speed as the air is exhaled forcefully. In this simple but extremely important maneuver the patient is asked to take a full deep breath in, then exhale fully and forcefully this is called a maximum forced expiratory maneuver. In tracing this maneuver the physician determines the maximum amount of air the patient can expel after the deepest inhalation. This amount is called the vital capacity.

As air is expelled the airflow is measured throughout the maneuver until the patient is unable to exhale further. One extremely useful measurement is of the greatest flow that can be obtained after the patient has inhaled fully and forcefully exhaled. This is termed peak expiratory flow rate or “peak flow.” This important and easily performed. Flow rates are recorded at the beginning, middle, and end of the forced exhalation maneuver and so is the amount of air expelled each second. As air is exhaled by the lungs it is the large bronchial tubes (large airways) that empty first with the smaller passages (small airways) contributing a greater share as exhalation continues and ends. In one second a certain amount of air should normally be exhaled with an expected increase as time increases. The one-second measurement is often a good reflector of the large airways and measurements toward the middle and end of the breath usually determine the condition of smaller air passages.

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