Allergy definition
Allergy can be described as a malfunction of the human immune system causing mild to severe reactions against normally harmless substances in the natural environment. Such substances are generally referred to as "allergens".
All of the risk factors for allergy are not known, but genetic and environmental factors play an integral role. People with a tendency to suffer from allergic conditions are said to be atopic.
Allergy can be antibody-mediated or cell-mediated. If the antibody responsible for an allergic reaction belongs to the IgE isotype, individuals are referred to as suffering from an IgE-mediated allergy.
Symptoms
Symptoms of allergy vary in complexity, severity and clinical manifestation. Exposure to an allergen can have an immediate effect. Symptoms can be mild or severe, including: itchy eyes, eczema, rhinitis, conjunctivitis, bronchoconstriction, vomiting and diarrhea and, in rare cases, anaphylaxis. Chronic reactivity can be seen as skin reactions (eczema) and/or respiratory reactions involving either or both the upper and lower respiratory symptoms. Ongoing lung tissue inflammation can be the reason for an asthma exacerbation seen after exposure to an offending allergen. Asthma exacerbations can also be brought about by events other than IgE-mediated reactions.
Clinical manifestations of atopic disease vary considerably as a result of the allergen involved, as well as the age of the allergic patient. During infancy, allergies to food (especially egg and milk) are the most common. After the age of 3, allergy to inhalants becomes predominant. Specific IgE antibodies often precede allergy symptoms, with clinical symptoms catching up over time.
Clinicians need to investigate all allergy symptoms and the possible underlying cause of the symptoms.
Allergy development
In its early stages, allergy can appear as a seemingly benign condition. For some patients an allergic condition gradually builds for several years before the patient experiences any symptoms. Other patients experience sudden, life-threatening anaphylactic shock following ingestion of certain foods or drugs, or an insect bite. Additionally, the clinical manifestations of some allergies start as eczema or gastrointestinal problems which can evolve into asthma, and respiratory symptoms such as hyperreactivity and obstruction of the airways.
IgE testing
Specific IgE blood tests can be performed without regard to the patient’s age, skin condition, medication utilization, as well as during pregnancy. IgE antibodies appear in human serum and plasma as a result of exposure and sensitization to a specific allergen. Measurement of circulating IgE provides an objective quantitative measurement of a patient’s sensitization to a specific allergen.
Phadia offers over 650 different allergens and 70 allergen components for sensitive and specific quantitative detection of allergen-specific IgE antibodies.
A final diagnosis of allergic disease should always be based on a combination of IgE test results and a patient’s clinical history. In general, the higher the IgE antibody value, the greater the likelihood of symptoms appearing.
See Case Study Felix for an example of how quantitative test results can help determine if a child has a good prognosis to outgrow a food allergy.