Dr Hesam Nabavizadeh Shiraz university of medicine Indication Allergy skin tests are widely used to help diagnose allergic conditions including Hay fever allergic rhinitis Allergic asthma ID: 1034192
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2. Diagnostic test in asthma and allergyDr Hesam NabavizadehShiraz university of medicine
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6. IndicationAllergy skin tests are widely used to help diagnose allergic conditions, including:Hay fever (allergic rhinitis)Allergic asthmaDermatitis (eczema)Food allergiesPenicillin allergyBee venom allergy
7. Drug AvoidancePrescription antihistamines, such as hydroxyzine .Over-the-counter antihistamines, such as loratadine .diphenhydramine ,chlorpheniramine, cetirizine .and fexofenadine .Tricyclic antidepressants, such as nortriptyline Certain heartburn medications, such as cimetidine and ranitidine.The asthma medication omalizumab (Xolair). This medication can disrupt test results for six months or longer even after quit using it. For comparison, most medications affect results for days to weeks.
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9. Skin TestAbout 15 minutes after the skin pricks, develop a raised, red, itchy bump (wheal) that may look like a mosquito bite. The nurse will then measure the bump's size and record the results.
10. Negative and Positive MarkerHistamine: In most people, this substance causes a skin response. If you don't react to histamine, your allergy skin test may not reveal an allergy even if you have one.Glycerin or saline: In most people, these substances don't cause any reaction. If patient do react to glycerin or saline, may have sensitive skin. Test results will need to be interpreted cautiously to avoid a false allergy diagnosis.
11. Allergy skin prick testingSkin prick test / positive result
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14. Positive Skin Test
15. Negative skin test
16. Blood testsIn addition to skin testing, some patients may require blood tests called specific IgE tests (also commonly known as RAST) to complete their allergy evaluation. Specific IgE tests can also be obtained in some situations where allergy skin testing is not appropriate. (a) when a patient cannot discontinue antihistamines or certain other medications that would affect skin test results. (b) patients with a condition called dermatographism (whereby scratching the skin causes hives)(c) patients with skin rashes/lesions that prevent from accurately reading the skin test results.
17. ImmunoassayNot influenced by medicationNot influenced by skin diseaseDoes not require expertiseQuality control possibleExpensive Skin testHigher sensitivityImmediate resultsRequires expertiseCheaperImmunoassay vs skin test for diagnosis of allergy
18. Primary AbSecondary AbEnzymeSample to be measuredSubstrateConcept of In Vitro IgE assays
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22. Patch testing Patch testIs generally done to see whether a particular substance is causing allergic skin inflammation (contact dermatitis). Patch tests can detect delayed allergic reactions, which can take several days to develop.During a patch test skin may be exposed to 20 to 30 extracts of substances that can cause contact dermatitis. These can include latex, medications, fragrances, preservatives, hair dyes, metals and resins.Patient wear the patches on your arm or back for 48 hours. During this time , patient should avoid bathing and activities that cause heavy sweating. Irritated skin at the patch site may indicate an allergy.
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25. Patch testing
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36. InterpretationA positive skin test means that patients may be allergic to a particular substance. Bigger wheals usually indicate a greater degree of sensitivity. A negative skin test means that patients probably aren't allergic to a particular allergen.Keep in mind, skin tests aren't always accurate. They sometimes indicate an allergy when there isn't one (false-positive), or skin testing may not trigger a reaction when you're exposed to something that you are allergic to (false-negative).
37. Food ChallengesThis is performed in selected individuals to confirm a food allergy or to determine if they may tolerate a food that they are currently avoiding. Incremental doses of the food are given to the patient starting with a very small quantity. Each dose is followed by a period of observation and assessment prior to receiving the next dose. Due to the risk of developing an adverse reaction, all food challenges are performed under physician supervision.
38. Drug ChallengeThis is performed in selected individuals to confirm a drug allergy or to determine if they may tolerate a drug that they are currently avoiding. Incremental doses of the drug are given to the patient starting with a very small dose. Each dose is followed by a period of observation and assessment prior to receiving the next dose. After receiving the final dose, the patient undergoes an additional observation period and final assessment.
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