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There are several methods for the diagnosis and assessment of allergies.
Skin testing
For assessing the presence of specific IgE antibodies, allergy skin testing, when possible, is the preferred method in comparison with various in vitro tests such as RAST because it is more sensitive and specific, simpler to use, and less expensive.
The typical method of diagnosis and monitoring of Type I Hypersensitivity is skin testing, also known as "scratch testing" and "prick testing" due to the series of pricks and/or scratches made into the patient's skin. Small amounts of suspected allergens and/or their extracts (pollen, grass, mite proteins, peanut extract, etc.) are introduced to sites on the skin marked with pen or dye (the ink/dye should be carefully selected, lest it cause an allergic response itself). The allergens are either injected intradermally or into small scratchings made into the patient's skin, often with a small plastic device. Common areas for testing include the inside forearm and the back. If the patient is allergic to the substance, then a visible inflammatory reaction will usually occur within 30 minutes. This response will range from slight reddening of the skin to full-blown hives in extremely sensitive patients.
After performing the skin test and receiving results, the doctor may apply a Hydrocortisone cream, also known as corticosteriods, to the test area to reduce discomfort (such as itching and inflammation)[citation needed].
Considerations with skin test
The skin prick test is the most preferred means of testing because of its simplicity, economic implications and its accuracy relative to the other tests available.
Interpretation of the results of the skin prick test is normally done by allergists on a scale of severity, with +/- meaning borderline allergies, and 4+ being of critical severity.
Theoretical concerns include how to choose patients, interpret results, and maintain safety. If a serious life threatening anaphylactic reaction has brought a pateint in for evaluation, some allergists will prefer a blood test to the skin prick. Skin tests may not be an option if the patient has widespread skin disease or has not avoided antihistamines for several days. Additionally, some patients may believe they have determined their own allergic sensitivity from observation, but a skin test has been shown to be much better than patient observation to detect allergy.
Some people may display a small delayed-type hypersensitivity (DTH) reaction which can occur up 6 hours after application of the allergen and last up to 72 hours but is often easily treated with anti-inflammatory creams. Interpretation by well-trained allergists is often guided by relevant literature which can offer calculation of 95% and 99% predicted probabilities using logistic regression revealed predictive decision points .
Another consideration with the application of previously un-encountered insect venom allergen is the theoretical possibility that this minute exposure can actually sensitize one to these allergen, causing the inception of a new sensitivity, but such a development is almost unheard of in clinical experience[citation needed]. For all these reasons skin testing should be offered by individuals with advanced training in the diagnosis and treatment of allergic disease.
Blood testing
This kind of testing is also known as a "total IgE count". In order to qualify type I hypersensitivity, this method measures the amount of serum IgE contained within the patient's serum. This can be determined through the use of radiometric and colormetric immunoassays. Even the levels the amount of IgE specific to certain allergens can be measured through use of the radioallergosorbent test (RAST). A leading RAST, which is a commercially available qualitative serological test employed for screening of allergic sensitization in patients with suspected allergic diseases, has a sensitivity of about 70.8% and a positive predictive value of 72.6% according to a large study.
In summary, a low Total IgE is not useful to rule out sensitization to common inhalant allergens. ROC curves, predictive values, and likelihood ratios are available, and they have shown high total IgE may indicate a high probability of sensitization but that further investigation is often still warranted with specific allergy tests to a panel of common inhalant allergens.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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