Editing Allergy (section)

==Diagnosis==
[[File:Allergy testing machine.jpg|left|thumb|An allergy testing machine being operated in a diagnostic immunology lab]]
Effective management of allergic diseases relies on the ability to make an accurate diagnosis.<ref>{{cite journal |author=Portnoy JM |year=2006 |title=Evidence-based Allergy Diagnostic Tests |journal=Current Allergy and Asthma Reports |volume=6 |issue=6|pages=455–61 |doi=10.1007/s11882-006-0021-8|pmid=17026871 |s2cid=33406344 |display-authors=etal}}</ref> Allergy testing can help confirm or rule out allergies.<ref name="ReferenceA">NICE Diagnosis and assessment of food allergy in children and young people in primary care and community settings, 2011</ref><ref name="ReferenceB">{{cite journal | vauthors = Boyce JA, Assa'ad A, Burks AW, Jones SM, Sampson HA, Wood RA, Plaut M, Cooper SF, Fenton MJ, Arshad SH, Bahna SL, Beck LA, Byrd-Bredbenner C, Camargo CA, Eichenfield L, Furuta GT, Hanifin JM, Jones C, Kraft M, Levy BD, Lieberman P, Luccioli S, McCall KM, Schneider LC, Simon RA, Simons FE, Teach SJ, Yawn BP, Schwaninger JM | display-authors = 6 | title = Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-sponsored expert panel | journal = The Journal of Allergy and Clinical Immunology | volume = 126 | issue = 6 Suppl | pages = S1–58 | date = December 2010 | pmid = 21134576 | pmc = 4241964 | doi = 10.1016/j.jaci.2010.10.007 }}</ref> Correct diagnosis, counseling, and avoidance advice based on valid allergy test results reduce the incidence of symptoms and need for medications, and improve quality of life.<ref name="ReferenceA"/> To assess the presence of allergen-specific IgE antibodies, two different methods can be used: a skin prick test, or an allergy [[blood test]]. Both methods are recommended, and they have similar diagnostic value.<ref name="ReferenceB"/><ref>{{cite journal | vauthors=Cox L | year=2011 | title=Overview of Serological-Specific IgE Antibody Testing in Children | journal=Pediatric Allergy and Immunology | volume=11 | issue=6 | pages=447–53 | doi=10.1007/s11882-011-0226-3 | pmid=21947715 | s2cid=207323701 }}</ref>

Skin prick tests and blood tests are equally cost-effective, and health economic evidence shows that both tests were cost-effective compared with no test.<ref name="ReferenceA"/> Early and more accurate diagnoses save cost due to reduced consultations, referrals to secondary care, misdiagnosis, and emergency admissions.<ref>{{cite web|title = CG116 Food allergy in children and young people: costing report|date =  23 February 2011 |url=http://guidance.nice.org.uk/CG116/CostingReport/pdf/English |archive-url=https://web.archive.org/web/20120117230445/http://guidance.nice.org.uk/CG116/CostingReport/pdf/English |archive-date=17 January 2012 |website = National Institute for Health and Clinical Excellence}}</ref>

Allergy undergoes dynamic changes over time. Regular allergy testing of relevant allergens provides information on if and how patient management can be changed to improve health and quality of life. Annual [[Allergy test|testing]] is often the practice for determining whether allergy to milk, egg, soy, and wheat have been outgrown, and the testing interval is extended to 2–3 years for allergy to peanut, tree nuts, fish, and crustacean shellfish.<ref name="ReferenceB"/> Results of follow-up testing can guide decision-making regarding whether and when it is safe to introduce or re-introduce allergenic food into the diet.<ref name="United States 2010">{{cite web|publisher = NIH|title = Guidelines for the Diagnosis and Management of Food Allergy in the United States: Summary of the NIAID-Sponsored Expert Panel Report|date = 2010|id = 11-7700|url = https://www.foodallergy.org/sites/default/files/migrated-files/file/niaid-clinician-summary.pdf|access-date = 1 April 2019|archive-date = 1 April 2019|archive-url = https://web.archive.org/web/20190401215258/https://www.foodallergy.org/sites/default/files/migrated-files/file/niaid-clinician-summary.pdf}}</ref>

===Skin prick testing===
<!-- Hidden text, as this links back to the same page, restore when main article is created - {{Main|Skin Test|l1=Skin testing}}-->
[[File:Allergy skin testing.JPG|thumb|right|Skin testing on arm]]
[[File:Skintest2.jpg|thumb|right|Skin testing on back]]
[[Skin test]]ing is also known as "puncture testing" and "prick testing" due to the series of tiny punctures or pricks made into the patient's skin. Tiny amounts of suspected allergens and/or their [[extracts]] (''e.g.'', pollen, grass, mite proteins, peanut extract) 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). A negative and positive control are also included for comparison (eg, negative is saline or glycerin; positive is histamine). A small plastic or metal device is used to puncture or prick the skin. Sometimes, the allergens are injected "intradermally" into the patient's skin, with a needle and syringe. 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&nbsp;minutes. This response will range from slight reddening of the skin to a full-blown [[Urticaria|hive]] (called "wheal and flare") in more sensitive patients similar to a [[mosquito bite]]. Interpretation of the results of the skin prick test is normally done by allergists on a scale of severity, with +/− meaning borderline reactivity, and 4+ being a large reaction. Increasingly, allergists are measuring and recording the diameter of the wheal and flare reaction. Interpretation by well-trained allergists is often guided by relevant literature.<ref name="pmid16164451"/>

In general, a positive response is interpreted when the wheal of an antigen is ≥3mm larger than the wheal of the negative control (eg, saline or glycerin).<ref>{{Cite web |title=Appropriate use of allergy testing in primary care - Best Tests December 2011 |url=https://bpac.org.nz/BT/2011/December/allergy-testing.aspx#:~:text=If%20the%20diameter%20of%20the,the%20age%20of%20the%20individual. |access-date=2024-04-19 |website=bpac.org.nz}}</ref> 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.<ref name="pmid11101180" />

If a serious life-threatening anaphylactic reaction has brought a patient in for evaluation, some allergists will prefer an initial blood test prior to performing the skin prick test. Skin tests may not be an option if the patient has widespread skin disease or has taken [[antihistamines]] in the last several days.

===Patch testing===
{{Main|Patch test}}
[[File:Epikutanni-test.jpg|thumb|[[Patch test]]]]
Patch testing is a method used to determine if a specific substance causes allergic inflammation of the skin. It tests for delayed reactions. It is used to help ascertain the cause of skin contact allergy or [[contact dermatitis]]. Adhesive patches, usually treated with several common allergic chemicals or skin sensitizers, are applied to the back. The skin is then examined for possible local reactions at least twice, usually at 48 hours after application of the patch, and again two or three days later.

===Blood testing===
An allergy [[blood test]] is quick and simple and can be ordered by a licensed health care provider (''e.g.'', an allergy specialist) or general practitioner. Unlike skin-prick testing, a blood test can be performed irrespective of age, skin condition, medication, symptom, disease activity, and pregnancy. Adults and children of any age can get an allergy blood test. For babies and very young children, a single needle stick for allergy blood testing is often gentler than several skin pricks.

An allergy blood test is available through most [[Medical laboratory|laboratories]]. A sample of the patient's blood is sent to a laboratory for analysis, and the results are sent back a few days later. Multiple allergens can be detected with a single blood sample. Allergy blood tests are very safe since the person is not exposed to any allergens during the testing procedure. After the onset of anaphylaxis or a severe allergic reaction, guidelines recommend emergency departments obtain a time-sensitive blood test to determine blood tryptase levels and assess for mast cell activation.<ref>{{Cite journal |last=Reinhold |first=Lauren |date=February 2023 |title=An Update on Test use Evaluation of Serum Tryptase Levels |url=https://www.jacionline.org/article/S0091-6749(22)01692-X/fulltext |journal=The Journal of Allergy and Clinical Immunology |volume=151 |issue=2|pages=AB10 |doi=10.1016/j.jaci.2022.12.038 }}</ref>

The test measures the concentration of specific [[IgE|IgE antibodies]] in the blood. [[Quantitative analysis (chemistry)|Quantitative]] IgE test results increase the possibility of ranking how different substances may affect symptoms. A rule of thumb is that the higher the IgE antibody value, the greater the likelihood of symptoms. Allergens found at low levels that today do not result in symptoms cannot help predict future symptom development. The quantitative allergy blood result can help determine what a patient is allergic to, help predict and follow the disease development, estimate the risk of a severe reaction, and explain [[cross-reactivity]].<ref>{{cite journal | vauthors = Yunginger JW, Ahlstedt S, Eggleston PA, Homburger HA, Nelson HS, Ownby DR, Platts-Mills TA, Sampson HA, Sicherer SH, Weinstein AM, Williams PB | display-authors = 6 |title=Quantitative IgE antibody assays in allergic diseases |journal=Journal of Allergy and Clinical Immunology |date=June 2000 |volume=105 |issue=6 |pages=1077–84 |doi=10.1067/mai.2000.107041| pmid = 10856139 |doi-access=free }}</ref><ref>{{cite journal | vauthors = Sampson HA | title = Utility of food-specific IgE concentrations in predicting symptomatic food allergy | journal = The Journal of Allergy and Clinical Immunology | volume = 107 | issue = 5 | pages = 891–96 | date = May 2001 | pmid = 11344358 | doi = 10.1067/mai.2001.114708 }}</ref>

A low total IgE level is not adequate to rule out [[Sensitization (immunology)|sensitization]] to commonly inhaled allergens.<ref name="pmid12911420"/> [[statistics|Statistical methods]], such as [[ROC curve]]s, predictive value calculations, and likelihood ratios have been used to examine the relationship of various testing methods to each other. These methods have shown that patients with a high total IgE have a high probability of allergic sensitization, but further investigation with allergy tests for specific IgE antibodies for a carefully chosen of allergens is often warranted.

Laboratory methods to measure specific IgE antibodies for allergy testing include [[enzyme-linked immunosorbent assay]] (ELISA, or EIA),<ref name=webmd>{{cite web|url=http://www.webmd.com/allergies/guide/blood-test|title=Blood Testing for Allergies|access-date=5 June 2016|website=[[WebMD]]|url-status=live|archive-url=https://web.archive.org/web/20160604101105/http://www.webmd.com/allergies/guide/blood-test|archive-date=4 June 2016}}</ref> [[radioallergosorbent test]] (RAST),<ref name=webmd/> fluorescent enzyme [[immunoassay]] (FEIA),<ref name="KhanUeno-Yamanouchi2012">{{cite journal | vauthors = Khan FM, Ueno-Yamanouchi A, Serushago B, Bowen T, Lyon AW, Lu C, Storek J | title = Basophil activation test compared to skin prick test and fluorescence enzyme immunoassay for aeroallergen-specific Immunoglobulin-E | journal = Allergy, Asthma, and Clinical Immunology | volume = 8 | issue = 1 | pages = 1 | date = January 2012 | pmid = 22264407 | doi = 10.1186/1710-1492-8-1 | pmc=3398323 | doi-access = free }}</ref> and [[chemiluminescence immunoassay]] (CLIA).<ref>Casas ML, Esteban Á, González-Muñoz M, Labrador-Horrillo M, Pascal M, & Teniente-Serra A (2020). VALIDA project: Validation of allergy in vitro diagnostics assays (Tools and recommendations for the assessment of in vitro tests in the diagnosis of allergy). In Advances in Laboratory Medicine (Vol. 1, Issue 4). Walter de Gruyter GmbH. https://doi.org/10.1515/almed-2020-0051</ref><ref>Bulat Lokas S, Plavec D, Rikić Pišković J, Živković J, Nogalo B, & Turkalj M (2017). Allergen-Specific IgE Measurement: Intermethod Comparison of Two Assay Systems in Diagnosing Clinical Allergy. Journal of Clinical Laboratory Analysis, 31(3), e22047. https://doi.org/10.1002/jcla.22047</ref>

===Other testing===
'''Challenge testing:''' Challenge testing is when tiny amounts of a suspected allergen are introduced to the body orally, through inhalation, or via other routes. Except for testing food and medication allergies, challenges are rarely performed. When this type of testing is chosen, it must be closely supervised by an [[allergist]].

'''Elimination/challenge tests:''' This testing method is used most often with foods or medicines. A patient with a suspected allergen is instructed to modify his diet to totally avoid that allergen for a set time. If the patient experiences significant improvement, he may then be "challenged" by reintroducing the allergen, to see if symptoms are reproduced.

'''Unreliable tests:''' There are other types of allergy testing methods that are unreliable, including [[applied kinesiology]] (allergy testing through muscle relaxation), [[cytotoxicity]] testing, urine autoinjection, skin [[titration]] (Rinkel method), and provocative and neutralization (subcutaneous) testing or sublingual provocation.<ref name="Allergy Diagnosis"/>

===Differential diagnosis===
Before a diagnosis of allergic disease can be confirmed, other plausible causes of the presenting symptoms must be considered.<ref>{{EMedicine|med|3390|Allergic and Environmental Asthma}} –
Includes discussion of differentials</ref> [[Vasomotor rhinitis]], for example, is one of many illnesses that share symptoms with allergic rhinitis, underscoring the need for professional differential diagnosis.<ref name="pmid16190503"/> Once a diagnosis of [[asthma]], rhinitis, anaphylaxis, or other allergic disease has been made, there are several methods for discovering the causative agent of that allergy.