Allergies are a common problem among children and adults across the globe. It is an abnormal reaction of the immune system to otherwise harmless substances (allergens). Some allergies result in mild symptoms that a person has to manage over months and years. But other allergies can be very severe and lead to serious symptoms, some of which may be life-threatening. An allergic reaction results in inflammation in the hypersensitive tissue. These inflammatory symptoms appear similar to chemical and mechanical injury, autoimmune diseases, infections and other pathological mechanisms. Therefore allergy testing is necessary to differentiate symptoms that are due to an allergy from other problems.
There are 4 different types of allergic reactions. All reactions are a combination of complex processes that occur within the body. It involves different cells and chemicals which work together to cause inflammation. It is important to realize that these processes are part of the immune system’s defense mechanism. Normally the reaction would occur when the body faces a threat in order to neutralize it and prevent any damage to the body.
However, in an allergy these reactions are abnormally initiated when there is no threat. For this reason an allergy is referred to as immune hypersensitivity since the immune system is abnormally sensitive to substances. Some reactions occur within a few minutes of being exposed to a trigger and is therefore referred to as immediate hypersensitivity. Other reactions occur within days after being exposed to an allergen and is known as delayed hypersensitivity.
Allergy testing involves verifying the a person does have an allergy, assessing the severity of the allergy and identifying the allergen (trigger). Sometimes an allergen cannot be conclusively identified. Allergens may be ingested (food or drink), inhaled or touched.
The medical consultation conducted by a doctor is an important part in the diagnosis of allergies. It incorporates both a thorough case taking and physical examination. The case taking will allow a doctor to identify the possible triggers (allergens) and symptoms indicative of an allergy that may have resolved by the time of the consultation. The physical examination allows the doctor to visibly verify the presence of certain symptoms that confirm an allergy. Further tests may be done in the doctor’s rooms or sent off to a laboratory for investigation.
A consultation with a doctor may be anywhere between 15 minutes to an hour. It is a snapshot in a person’s life. Symptoms that may have developed and resolved over hours, days and weeks may not be able to be verified by a doctor in person. Instead a symptom diary assists the doctor in understanding and assessing the chain of events and symptoms that arises over time. Symptoms are recorded by the patient in a diary and includes details about what food is eaten or what possible substances were encountered that may correlate with the symptoms.
An elimination diet is a very effective method of identifying the possible food allergen that may be a problem for a specific person. It is usually supervised by a doctor and runs over a period of weeks or months. The elimination diet involves removing certain foods that may be the problem as identified during the case history and from the symptom diary. If the symptoms of the allergy resolves or improves when a food is eliminated but returns once the food is re-introduced into the diet, then this confirms that the food in question is indeed a trigger.
Allergy Skin Test
These tests are used to verify an allergic reaction to a substance by monitoring skin reactions. There are three types of allergy skin tests:
- Skin prick test
- Intradermal test
- Skin patch test
Skin Prick Test
The skin prick test is a superficial test that is done on the outermost layer of the skin known as the epidermis. Different areas are marked on the skin and a small amount of each allergen (the extract of the allergen) is placed on it. Then the skin is pricked so that the allergen can enter the epidermis. If a person is allergic to one of these allergens, there should be a visible reaction on the skin within a few minutes to an hour.
For a more sensitive variation of the skin prick test, your doctor may choose the intradermal test. Here a small quantity of the allergen is injected under the skin. This allows the allergen to be introduced deeper into the body than the skin prick test. A skin reaction would be evident usually within 20 minutes if a person is allergic to the substance that was injected.
Skin Patch Test
The skin patch test is performed by applying a patch containing the allergen to the skin. It is used to identify delayed hypersensitivity which may only be evident within 48 to 72 hours after exposure to the allergen. The skin will become irritated as antibodies react to the allergen(s) on the patch. There is itching and redness of the skin if you are allergic to the substance which then confirms the allergy.
Allergy Blood Test
An allergy blood test is another method for confirming certain allergies. It works by detecting the presence of allergen-specific antibodies in the bloodstream. There are pros and cons to allergy blood tests over skin tests and often a doctor may consider both types of tests when attempting to verify an allergy. Some of the allergy blood tests that may be done include:
- Total IgE
Total IgE Test
A total IgE assesses the amount of IgE (immunoglobulin E) in the blood. This immunoglobulin is closely related to allergies. The total IgE verifies whether an allergy is present but does not indicate the allergen to which you may be reacting. IgE levels may also be raised with certain parasitic infections.
Allergen-Specific IgE Antibody Test
This test is also known commonly as an allergen screen. It measures the presence of immunoglobulins to specific allergens. In this way the test will reveal the allergens to which a person is reacting. These newer IgE-specific tests have replaced the older RAST test although it is still sometimes referred to as a RAST (radioallergosorbent test) by some medical practitioners.