In a subject presenting symptoms characteristic of asthma, the allergic cause must be identified. This diagnosis can be conducted by an allergist in children as well as in adults
The different stages of allergic diagnosis
The interview is the first stage in diagnosis. The aim is to confirm the existence of an allergic state and establish a preliminary list of allergens which may be causing the observed symptoms.
The main areas covered are:
- History of the symptoms (how long ago they first appeared, what they are like and when they occur, any triggering factors already identified)
- Family history of allergy (any close relative who is allergic) or in the patient's own history (allergy during childhood)
- The patient's general environment (living and working conditions as well as climate)
- Details about lifestyle and habitats (home, workplace, pets, eating habits)
- Activities (occupation, pastimes)
It may take more than one consultation to gather all of the information required.
As well as a general examination (weight, blood pressure, etc.), the specialist examines in detail those organs in which allergic symptoms commonly manifest themselves (the skin, lungs, nose and bronchi). This allows the allergist to assess the impact of the allergy and indicates possible further tests that might fall outside the allergic field (pulmonary function tests in asthma).
RESPIRATORY FUNCTION TEST
This is essential to assess the extent of the ventilatory disorder. The test comprises a spirometry and flow volume curve analysis. In certain cases, it will be necessary to measure the functional residual capacity or resistance of the airways by plethysmography.
PEAK FLOW METER
This asthma monitoring tool can be used in the home or at the doctor's practice. It measures the peak flow (PF) in litres per minute.
CAREFUL! If the PF is very low, the patient should see a doctor immediately or attend an accident & emergency unit. Examination of the trend in PF values is an excellent indicator of the asthma's stability.
SKIN TESTING (PRICK TESTS)
After the interview and the physical examination, a list is established of the allergens most likely to be responsible. This list will help determine skin testing.
What does skin testing entail?
The point of a skin test is to try to reproduce on a very small scale on the patient's skin the allergic reaction in its "immediate hypersensitivity" form (the allergic reaction appears immediately after contact with the allergen involved).
The prick test:
- A drop of the suspected allergen is placed on the forearm or back, and then a tiny puncture is made in the skin at the centre of the drop to allow the allergen to penetrate the dermis and provoke the allergic reaction
- The results can be read after 20 minutes: a hypersensitivity reaction results in redness of the skin resembling a mosquito bite with oedema (swelling) and itching.
- The severity of the reaction is evaluated compared with the reaction caused by a "control" substance (a "control" substance causes a reaction in all individuals without exception and makes it possible to learn the degree of severity with which the body of the patient reacts).
This technique is fast, painless, reproducible over time and well-tolerated, even by very young children. It is the most commonly used method.
When the prick tests cannot be interpreted or are negative although the symptoms persist, the allergist may call on a blood test. Identification of the specific IgE antibodies will enable the allergen in question to be identified.
NON-SPECIFIC PROVOCATION TESTS
They enable measurement of non-specific bronchial hyperreactivity and are practiced by inhalation of metacholine.
SPECIFIC PROVOCATION TESTS
If there is a discrepancy between the clinical tests and the blood tests, the allergist can perform a bronchial provocation test.