Asthma Helpline  



Diagnosis of asthma

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Skin allergy tests:

Skin tests are main tool in diagnosing allergies all over the world. It is out patient procedure and patient can go to school or office after the test. Each and every patient has different allergy profile which can be known by the skin allergy tests.

Identification of allergen triggers can assist in formulating an avoidance strategy. A trial of allergen avoidance may be diagnostic and therapeutic.

Mechanism of skin allergy testing:

Cells and antibodies which are responsible for allergies are present under the skin as well as other parts of the body. If an allergen to which patient is allergic is applied to the skin a reaction occur and a wheal is formed. The size of the wheal is measured to grade the severity of allergy.

There are number of ways to perform skin tests:

  • Patch test  ( used mainly for diagnosing contact dermatitis)

  • Scratch test

  • Skin prick test

  • Intradermal test

  • Skin end point titration

  • Parasite- kustner test ( Passive transfer test)

RAST (Radio allegrosorbent technique):

This test detects allergen specific IgE in the serum of the patients. The results of the tests correlate well with the skin allergy tests. One sample of the serum can be used to test many allergens. This test has many benefits over the conventional skin allergy tests. It can be used where the skin allergy tests cannot be performed like young children, severe atopic dermatitis, dermatographism, history of extreme sensitivity, patients afraid of multiple injections.

The result of RAST is not influenced by drugs while skin tests are suppressed by anti allergic drugs and steroids.
There is no risk of anaphylaxis with RAST.

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Complete Blood Count (CBC):

CBC is done to rule out tropical pulmonary eosinophilia and other infections.

Chest X-Ray:

Chest X-ray is done if there is suspicion of presence of some other disease like infection, large airway lesions, obstruction by foreign object or heart disease. It is also done if a patient is not improving after taking asthma medication.

Echocardiogram (ECG):

This test is used if congestive heart failure is suggested based on history and physical examination findings.

Gastroesophageal reflux assessment:

A barium swallow and 24-hour pH probe is done to diagnose gastroesophageal reflux disease (GERD), especially if a patient is not responding to asthma therapy.

If a patient has prominent symptoms of GERD, medical therapy is often tried without performing these tests.     

Nasal examination:

Nasal examination is also done if they are suspected of contributing to the asthma severity.


1. Direct and indirect laryngoscope is indicated if any laryngeal abnormality is suggested.

2. Cardiopulmonary exercise testing is indicated if the cause of dyspnea (breathlessness) cannot be determined.

last edited 18-7-2010

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