Hyperreactivity
Hyperreactivity to everyday irritants and stimuli may be IgE mediated (IgE allergy) or non-IgE (hyperreactivity). Distinguishing between the two types of hyperreactivity may influence the treatment strategy for a patient. Examples of hyperreactivity diseases and their triggers are listed below.Table 1: Triggers of hyperreactive diseases
Symptoms | IgE allergy Specific IgE triggers | Non-IgE hyperreactivity Non-specific triggers |
Anaphylaxis | Animal dander | Acetylsalicylic acid (Aspirin) |
Asthma | Food allergens | Cold air |
Conjunctivitis | Insect venom | Exercise |
Gastrointestinal disturbances | Mould spores | Pollution |
Rhinitis | Pollen | Pressure |
Urticaria | Temperature | |
Strong odours | ||
Water |
IgE allergy most frequently begins in early life and can last a lifetime. Non-IgE hyperreactivity tends to appear later in life. Hence, tests for IgE allergy tend to be most useful in children and young adults.
Hyperreactive diseases present differently according to age.
· In the neonate, dermatological symptoms and IgE-mediated conditions caused by foods are the most common.
· Later in childhood, airways symptoms appear (as a result of airborne allergens).
· In older children, symptoms from the airways prevail, with an increasing frequency up to the age of 10 to 15 years.
· In adults, hyperreactivity from the airways still constitutes the majority of allergic problems, but after the age of 30 an increasing number of patients experience skin reactions, non-IgE-mediated reactions from the airways, and non-specific symptoms from the connective tissue of the gastrointestinal tract, brain etc. Venom allergy most often appears in adults.
Tests used in the diagnosis of IgE-mediated allergy
Once evidence of hyperreactivity is established, allergy testing plays a significant role in the diagnosis of allergy (Table 2). It is important to note that an allergy test cannot have 100% specificity and sensitivity. Changing the cut-off level to improve one parameter will often worsen the other parameter. Hence, cut-off levels are set to maximise both sensitivity and specificity.
Table 2: Testing for IgE-allergy
Symptoms characteristic of IgE-allergy | Questionnaire, case history, clinical history |
Verify hyperreactivity | Hyperreactivity provocations, elevated eosinophil levels in blood or target organ. (If patient shows no reaction to hyperreactivity provocations, look for another disease.) |
Search for allergens | Small scale (if skin prick test is not available): total IgE, specific IgE to allergen panels. Specialty scale: standard and additional skin prick tests; specific IgE, histamine release, environmental analysis, allergen provocation in target organ. |
Positive allergy test (specific IgE) | Mild/Moderate/Severe IgE allergic hyperreactivity condition verified. |
Negative allergy test (non-specific IgE) | Mild/Moderate/Severe non-IgE allergic hyperreactivity condition verified. |
Total IgE
In the routine investigation of allergy, total IgE correlates poorly with symptoms of disease. Total IgE can be used as a guide to manage severe atopic dermatitis, but is not of use in allergic rhinitis and asthma. It can be used to assess patients with allergic bronchopulmonary aspergillosis. Elevated IgE can be seen in immunodeficiency as well as parasitic infections.
Allergen-specific IgE
Specific IgE may be determined from a range of allergens, using a non-isotopic variation of the radioallergosorbent test (RAST®). The results are not affected by medications.
The sensitivity and specificity of RAST® varies widely with the allergen being tested, with many published diagnostic cut-offs, though these may vary in different populations.
Hyperreactive diseases present differently at different ages:
· In children under 2 years of age, atopic dermatitis and food allergy are most common. Egg and peanut are the most common food allergens leading to disease at present.
· A variety of symptoms can start in the first 2 years of life, but typically manifest around 4 to 5 years of age with allergic rhinitis and/or asthma.
· Asthma presentation increases until the late teens, though new allergic disease after the teenage years is uncommon. In adult life, many new onset allergies cannot be demonstrated to have IgE as the cause. These are best termed sensitivities, as their pathologic basis is often uncertain.
· Venom allergy most commonly presents in adulthood, and reactions in those over 50 years of age may lack Cutaneous features (e.g. isolated hypotension)
Testing for IgE allergy
For example: allergic rhinitis, atopic dermatitis, acute food reactions (< 2 hours) Although RAST tests are available for a range fo allergens, Medicare Australia limits rebates based on the number, type and frequency of tests. An extended RAST panel can be performed for an additional fee.
Extended RAST® Food Panel
Almond, Banana, Cashew, Codfish, Cow’s milk, Egg white,Hazel nut, Mango, Peanut, Rice, Sesame seed, Shrimp (prawn), Soybean, Walnut.
Extended RAST® Inhalant Panel
To order please request extended RAST® Tests
Extended Food RAST®
Extended Environmental RAST®
Skin prick tests
Skin tests for a range of allergens (Table 3) are usually performed on the volar aspect of the forearm. Sullivan Nicolaides Pathology performs a standard panel for children (2 to 16 years), and one for adults. Antihistamines and neuropsychiatric medications, amongst others, may cause false negatives. Antihistamines should be avoided 4 days prior to testing.
As with RAST®, skin test sensitivity and specificity varies widely with the allergen. The sensitivity of the skin tests is higher than RAST®, although specificity can be much lower.
Reference
Stephen T. Holgate and Martin K. Church. Chapter 11, Diagnostic Tests for Allergy. Allergy, Gower Medical Publishing, London, 1993.
Table 3: Skin prick test allergen panels
Children 2–15 Years | |
Animal Food Insect: Mite Pollen: Control | Cat pelt Cow’s milk, egg, peanut Dust mite D pteronnysinus Grass Southern grasses (Bermuda, Johnson,Kentucky, Blue, Orchard, Red top, Sweet vernal,Timothy) Histamine, Negative |
Adults | |
Animal Food Insect: Mite Mould Pollen: Pollen: Tree Polleen: Control | Cat pelt, Dog dander Cod fish, cow’s milk, egg, peanut, prawn/shrimp, soybean, wheat Dust mite D pteronnysinus Alternaria alternata, Aspergillus fumigatus Hormodendrum cladosporioides, Pencillium notatum Grass Bahia grass, Plantain, Perennial rye grass, Southern grasses (Bermuda, Johnson, Kentucky, Blue, Orchard, Red top, Sweet vernal,Timothy) Acacia, Eucalyptus, Pine mix (lodgepole, Western yellow) Weed Ragweed mix (Giant, short) Histamine, Negative |
New advances in allergy testing are now available
Phadia ImmunoCap®ISAC
The Phadia ImmunoCAP®ISAC system is one of the most important recent advances in laboratory allergy diagnostics. It now allows us to determine, with a high level of accuracy and precision, specific IgE antibodies to a far wider range of allergens, including those that could not previously be tested for, and those present at low levels. We can now test for 103 clinically important allergen molecules from 47 different allergens.
Through this extended range of tests we have the ability not only to identify the allergens to which a patient is sensitive, but also, in some cases, to estimate the severity of the reaction or the level of tolerance to certain foods. It is a particularly useful test to assess whether a child may be growing out of their food allergies.
The test is performed on a routine blood sample that can be collected at any SNP collection centre. Results are not affected by medications. This test if not Medicare rebatable.
For more information visit:
http://www.snp.com.au/patient-services/health-library/allergy-tests.aspxDr Daman Langguth FRACP FRCPA
T: (07) 3377 8666
Correct at time of publication June 2012
© Sullivan Nicolaides Pty Ltd 2012
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