It is essential for successful treatment that the allergens responsible for the symptoms are accurately identified. There are different ways to arrive at a diagnosis. The case history is extremely important in all allergy investigations. Based on what the patient tells about his or her symptoms, the doctor decides what tests, if any, should be carried out.
The case history should form the basis for all allergy investigations. In order to give the doctor an idea of the mechanisms and allergens causing the trouble, the doctor will question the patient or ask him/her to fill in a questionnaire. It is important to know when and how the symptoms developed. Also important is the relationship to seasons, damp weather, physical activity, certain foods, etc. Knowledge of personal habits such as smoking, occupation, hobbies, etc., will be necessary and some information about the home can be important (e.g., whether there are pets, are fitted carpets in the house or if cleaning aggravate symptoms). A favourite cologne or perfume can be the cause of allergic conjunctivitis, while soap may be the cause of chronic Eczema. Fingernail polish may cause Eczema of the upper eyelids. In nasal allergies, the case history alone may give enough information to settle the diagnosis and the doctor can then decide which measures to take to help the patient. In more complicated cases, however, for the investigations may be performed to get a final diagnosis.
Many doctors to identify allergens responsible for the symptoms use skin test procedures. There are several methods of skin testing. The most significant skin test are those which correlate with the patient’s history (i.e. a positive skin test for ragweed is not significant if ragweed never causes allergy symptoms).
Drops of the suspected allergens are put on the skin of the forearm and the skin is either pricked or scratched (Prick or Scratch Test) through the drop. Suspected allergens can also be injected into the skin of the back (intradermal skin test). After 15 to 20 minutes, if there is an allergy to one or more of the substances, around weal with a flare (red swelling) forms on the spots where the substances were injected. This may identify and confirm the allergy.
However, besides causing the patient some trouble, the intradermal skin tests may not be very reliable. Drug treatment for the allergic symptoms in the 72 hours prior to the skin test may invalidate the results, and skin testing in small children is both inconvenient and unreliable.
Patch testing is used in the investigation of allergic contact dermatitis. The test is performed by using a small piece of blotting paper, moistened with the suspected substance, or a prepared strip containing various standard allergens. The paper or strip is tapped to an area of healthy skin for 24 to 48 hours. If you are allergic to the substance tested, eczema will be seen where the test substance has been in contact with your skin.
Provocation and Elimination Tests
These tests are performed in the eyes and nose for hay fever sufferers. A highly diluted allergen extract is dropped into the eyes or nose or is inhaled. The test is continued in this way, using more concentrated allergens until the allergic symptoms are provoked. This shows that the tested allergen is responsible for the patient’s symptoms.
When food allergy suspected, different foods (usually those that are most commonly associated with allergy) are eliminated to see if the symptoms disappear. They are we introduced into the diet one by one, to see, if any of them causes a return of the symptoms. The most common food sensitivities are to cow’s milk, corn, wheat, eggs, and soy.
The skin and provocation tests, apart from being inconvenient to the patient, have other disadvantages too.
IgE plays an important role in allergic rhinitis, allergic asthma and in some forms of Eczema. Detecting and accurately measuring the amount of IgE may be of great importance when diagnosing allergies.
Because of the limitations and disadvantages associated with the skin and provocation tests, there has been a need for more convenient and reliable method. Today, there are laboratory tests available that accurately measure either the total amount of IgE in the blood, which indicates if your symptoms are of allergic origin or specific IgE, which tells the doctor as which allergens are causing the trouble. Another allergy blood test is called RAST (Radioimmuno Absorbent Test). These blood tests are significant primarily if the identified substances cause patient symptoms. RAST is especially helpful in very young children.
Another test which is commonly used is called “Absolute Eosinophil Count”. It is a type of WBC (White Blood Cell) which gets increased in case of any allergic condition.