Exercise-Induced Asthma Workup

In general, exercise-induced asthma (EIA) is diagnosed clinically and may not need any further laboratory studies, imaging studies, or other tests and procedures. Laboratory evaluation is reserved for equivocal cases, for treatment failures, and to narrow the differential diagnosis when it seems reasonable. Testing may then be appropriate to differentiate EIA from cardiac conditions, vocal cord and upper airway obstructive conditions, allergic conditions, and psychiatric conditions when these are strongly considered in the differential diagnosis.

Imaging studies are often not indicated in the evaluation of routine EIA, but they may be useful for evaluating other possibilities in the differential diagnosis.

A complete blood cell count and differential can help in the assessment of the likelihood of infection by analysis of the patient's white blood cells and by evaluation of the eosinophil counts (for allergy).

Assessing the immunoglobulin E (IgE) level helps in determining the likelihood of allergic disease. If the diagnosis is uncertain, performing a nasal swab for the presence of eosinophils is helpful in identifying the role of allergic rhinitis.

Skin allergen testing or a radioallergosorbent test (RAST) can be used to help identify specific allergens to promote patient avoidance or immunotherapy, if indicated. Either method has been used extensively in atopic workups. In young children, RAST testing may be preferable, owing to the relative ease of administration, but this is a less specific test, and therefore, skin testing may be preferred in general.

An erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) may help in the evaluation of inflammatory and infectious conditions. Sputum analysis and culture can be used to help identify the presence of infection and treatment options for strains of resistant organisms.

Thyrotropin levels can be used to help evaluate the potential of patient thyroid dysfunction in the likelihood that anxiety is mimicking the symptoms of asthma.

Chest radiography is used to evaluate for signs of chronic lung disease (eg, hyperexpansion, scarring, fibrosis, hilar adenopathy), for congestive heart failure and/or valvular heart disease (eg, chamber enlargement, pulmonary edema, vascular or valvular calcification), and for a foreign body. Lateral neck radiographs/soft-tissue penetration can also evaluate the upper airway for a foreign body or obstruction

Go to Imaging in Asthma for complete information on this topic.

Echocardiography may be used to evaluate for cardiac valvular abnormality or global contractile function, as well as dysrhythmia, cardiomegaly, or other heart disease that may manifest during exercise.

Laryngoscopy can be performed to evaluate for foreign body or other obstruction in the upper airway. Postexercise laryngoscopy can be used to evaluate for vocal cord dysfunction, a condition often mistaken for EIA. Vocal cord dysfunction manifests as stridor with exercise due to paradoxical contraction of the vocal cords with inspiration; this condition can be evaluated via laryngoscopy after an exercise challenge.

Various challenge tests exist that can be used to formalize the diagnosis of EIA. A formal diagnosis is often not critical, clinically, but in recent years, the US Olympic Committee (USOC) has required a positive challenge test to be documented for an athlete to qualify for the use of controlled substances that aid in ameliorating the symptoms of EIA. This requirement has resulted in new studies that have been used to validate some of these assessment tools, whether they are field challenges, treadmill testing, or new techniques such as eucapnic voluntary hyperventilation (EVH). ^{[6, 5, 7]} At present, the USOC requires EIA to be diagnosed via EVH in order for preventive and treatment-related medications to be used in competition.

Treadmill exercise challenges with preexercise and postexercise pulmonary functions

This type of testing formalizes an aerobic challenge and provides an objective measure of the degree of bronchospasm that results from the exercise. The results can help the physician to clarify the diagnosis and to enforce the treatment; the results can also be used to evaluate success of the treatment.

Before the exercise challenge, the patient's baseline pulmonary function levels should be obtained (preferably forced expiratory volume in 1 second [FEV₁]; forced vital capacity [FVC], or FEV₁/FVC; or, less ideally, peak expiratory flow rate [PEFR]). The exercise challenge involves exercising the athlete on a treadmill until his or her heart rate reaches 70-85% of the maximum predicted heart rate. This is maintained for 6-10 minutes, at which time the exercise is stopped. Pulmonary function levels are measured every 2-10 minutes for 15-30 minutes and then compared with the baseline measurements.

Any drop from the baseline that is greater than or equal to 10%, on any postexercise measurement, indicates EIA. Severity of disease can be classified as follows:

• Mild - Decrease of 10-20% from baseline

• Moderate - Decrease of 20-40% from baseline

• Severe - Decrease of greater than 40% from baseline

Informal exercise challenge

An informal exercise challenge can be substituted for the above procedure, but without monitoring the heart rate, the level of work is not reliable.

Pulmonary function testing

Pulmonary function testing can be used to evaluate baseline pulmonary function or allergic asthma and to categorize pulmonary function as obstructive or restrictive disease.

Bronchoprovocation testing

Bronchoprovocation testing, as used with general asthma, methacholine, histamine, or cold air challenges, can be used to assess asthma. However, if the results are positive, they are indicative of asthma in general, not specifically EIA.

A study of 46 children with exercise-induced asthma-like symptoms reported that a combination of the methacholine test, followed by the mannitol test, gives the highest return to identify bronchial hyper-responsiveness in children for the diagnosis of exercise-induced asthma or bronchospasm. The combination of methacholine test and mannitol tests detected bronchial hyper-responsiveness in all of the children in whom bronchial hyper-responsiveness (BHR) was found (93.5% of all the children) compared to the exercise challenge testing which detected BHR in 23.90%, the bronchodilator testing which detected BHR in 21.7%, mannitol testing which detected BHR in 80% and methacholine testing which detected BHR 91%. ^{[19, 20]}

Eucapnic voluntary hyperventilation

Eucapnic voluntary hyperventilation (EVH) is a technique believed to be more sensitive and more accurate for diagnosing EIA. ^{[6, 7]} Furthermore, EVH can be applied in a laboratory setting and altered to mimic the environmental conditions of the sport in question.

Go to Peak Flow Rate Measurement for complete information on this topic.