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Establishing the diagnosis of asthma often occurs over a period of time and can be tricky particularly in infants and children younger than five. The clinical presentation of childhood asthma can vary significantly from children whose only symptom is coughing to children who are persistent wheezers and have difficulty breathing. Moreover, traditional pulmonary function tests such as spirometry, that are routinely used to diagnose asthma in adults and older children are very difficult to perform in infants and children younger than age five.

In general, the diagnosis of childhood asthma is based upon the child's medical history (e.g., signs and symptoms) and a physical examimination. Several diagnostic tests may also be performed to help the doctor establish the diagnosis of asthma and rule out other conditions that may cause similar symptoms.

Radiological Studies

• Chest X-ray helps to exclude other diagnoses (asthma does not cause changes in the x-ray)
• Sinus X-rays to exclude sinusitis
• X-rays of the gastrointestinal tract to rule out gastroesophageal reflux disease (GERD)

Laboratory Evaluation

• Complete blood count (CBC)
• Serum eosinophil count - a "marker" of allergies
• Serum IgE antibody levels - elevated levels of serum IgE antibodies suggests an allergic state
• Arterial blood gas (ABG) analysis - once common, this test is now usually reserved for asthmatics who are very ill and are at risk of requiring mechanical ventilation (intubation)
• Skin testing for allergens
• Sputum testing

Pulmonary Function Tests

Pulmonary function testing (PFT) can be used to make a diagnosis, to assess the response to therapy, and to monitor the course of the disease. Also known as spirometry, this is a test that is performed to evaluate and measure lung function. Spirometry is a non-inavasive test that uses a device called a spirometer to measure the amount of air that is blown out of the lungs. During the test, the patient is asked to take a deep breath and then quickly blow it out into a mouthpiece that is attached to the spirometer until all of the air has been expelled from the lungs.

The following parameters of lung function are measured with spirometry:

• Forced Expiration Volume in One Second (FEV1) - This is a measure of the amount of air that can be expelled from the lungs in one second (usually decreased in asthma).
• Forced Vital Capacity (FVC) - This is a measure of the total amount of air that can be expelled from the lungs in a single breath.
• The FEV1/FVC ratio - This number is calculated by dividing the FEV1 by the FVC.
• Forced expiratory flow 25%- 75% (FEF 25-75)- the amount of air expelled from the lungs during the middle-half of the forced vital capicity test (usually decreased in asthma).
• Peak expiratory flow rate (PEFR)- usually decreased in asthma.

Pulmonary function tests are usually administered first without any medications, then again after various doses of bronchodilator medications to measure the difference in results. This test may be difficult to perform for infants and children under age five.

Peak Flow Monitoring