Southern Derbyshire Shared Care Pathology Guidelines. Allergy Testing in Adults

Transcription

1 Southern Derbyshire Shared Care Pathology Guidelines Allergy Testing in Adults Allergy Tests are not diagnostic of Allergy Purpose of Guideline How to obtain an allergy-focussed clinical history When allergy testing is appropriate Deciding whether to do skin test or specific IgE blood test What the results mean Background Allergy is any abnormal immune-mediated response to an antigen This guideline is about IgE-mediated or atopic hypersensitivity (or Immediate/Type 1allergy) Allergic symptoms usually respond to anti-histamines and avoidance of the trigger Type 4 Allergy causes dermatitis and eczema delayed, cell-mediated Allergy and Intolerance are different o Allergy causes typical symptoms o Intolerance is not immune-mediated (mechanisms mostly unknown) o Intolerance tests don t exist Mechanism Clinical presentation Tests to consider (to support clinical history) Type 1 / IgE-mediated allergy Type 4 / cell-mediated allergy Intolerance Urticaria, angioedema, anaphylaxis, bronchospasm, rhinoconjunctivitis Eczema, contact dermatitis Wide variety of symptoms other than those above Serum Specific IgE (RAST) Skin prick test Patch test None available (beware of non-validated tests) Obtaining a useful clinical history 1. Are the symptoms consistent with IgE-mediated allergy? Urticaria Angio-oedema Wheeze Rhinoconjunctivitis Anaphylaxis Authorised by Julia Forsyth Page 1 of 5

2 2. Is there a history of atopy? Atopic people get atopic allergies Drug or insect sting allergies can happen to anyone 3. Is there a credible trigger? Timing (usually minutes, rarely >2 hours after exposure) Consistent reaction on exposure (e.g. seasonal) Multiple unrelated triggers usually means it is none of these 4. Could this be spontaneous (idiopathic)? Consider this when (1) is present without (2) or (3) Important scenarios: Spontaneous (idiopathic) urticaria / angio-oedema is common in adults. This occurs mainly in females and attacks may be associated with infection, stress, pre-menstrual, physical triggers (e.g. pressure of tight clothing, heat, cold). Allergy tests are not useful unless there is a strong candidate allergen suggested by the history. Angioedema without urticaria: check for ACE inhibitors. These drugs may cause facial, oral, pharyngeal swelling even after years of uneventful treatment. It is not a drug allergy. Some useful facts about common allergens House Dust Mite: Symptoms are often worse in the night and first thing in the morning and tend to improve in hot or cold climates where the mite cannot survive. Tree, grass, weed, moulds Seasonal timing can often identify specific allergen; Trees March-April Grass May-September Weeds autumn Moulds perennial or autumn symptoms Wheat allergy Wheat intolerance is common, wheat allergy isn t. Consider wheat-exercise induced allergy, where symptoms occur only on exertion after eating wheat. Also consider testing for Coeliac Disease. Oral allergy syndrome Symptoms localised to oropharynx occuring only with fresh fruit and vegetables in patients with Spring hay fever. Selecting the appropriate test This will depend on the clinical history ie, what has the patient been exposed to when symptoms occurred. A useful guide to test selection based on clinical history is shown below. Authorised by Julia Forsyth Page 2 of 5

3 Clinical Symptoms Asthma unresponsive to conventional treatment Seasonal Rhinitis Perennial Rhinitis Food allergy Urticaria Severe allergies Anaphylaxis Suggested allergy requests House Dust Mite, Animals danders (specify which eg, dog, cat), Grass or Tree Pollen (for seasonal exacerbation) NB, Smoke, perfume etc. are irritants, not allergens. Grass Pollen, Tree Pollen, Weed mix House Dust Mite, Animals danders, Moulds and fungal spores Identify on clinical history. If a large number of foods suspected, consider whether any are actually plausible. Often non-allergic. Testing only if allergy strongly indicated on history. Preferably discuss before testing. Check Mast Cell Tryptase as soon as the patient is stabilised. Allergy testing not indicated at acute presentation All patients presenting with anaphylaxis should be referred to an allergy clinic to identify the cause 1 Commonly available specific IgE tests FOODS Dairy: Milk, Egg, Cheese Nuts: Peanut, Almond, Brazilnut, Hazelnut, Cashew, Pecan, Pistachio, Walnut Fish: Fish Mix (Contains Cod, Shrimp, Tuna, Salmon, Blue Mussel- also available individually), Crab, Haddock, Oyster Fruit & Vegetables: Apple, Banana, Kiwi, Strawberry, Tomato, Celery Other foods: Soya, Wheat, Sesame, Yeast AERO ALLERGENS Animals & Mites: Cat, Dog, Horse, House dust mite Pollens: Timothy grass, Birch tree, Aspergillus Fumigatus, Cladsporium, Alternata alternaria WASP & BEE VENOM TRYPTASE Released by mast cells during allergic reaction, may be greatly raised in anaphylaxis Increased baseline levels may indicate mastocytosis a rare cause of allergy-like reactions OTHERS: Less common allergens are also available upon request. Please contact us with as much clinical detail as possible. Laboratory contact: Sapho Oliwiecki (Immunology Lead Biomedical Scientist) on or [email protected] Authorised by Julia Forsyth Page 3 of 5

4 Interpretation of results Grade Units (Ku/l) Interpretation 0 <0.35 Negative Weak positive Positive Positive Strong positive Strong Positive 6 >100 Strong Positive FAQ s. Does a negative test exclude allergy? No Does a positive test prove allergy? No. The diagnosis is made clinically, and the allergy test is used to support this Does a high grade or level of specific IgE mean severe allergy? No. The higher the level of specific IgE the more likely it is to cause allergic symptoms. These can be of any type and severity. The severity of a reaction is multifactorial and generally not predictable. For further clinical advice and interpretation of results or to discuss your patient, please contact the relevant clinician. Do I need to discuss or refer my patient? Most allergic disease can be successfully managed in primary care, and there are many guidelines to help. Discussion or referral can help to: select appropriate tests confirm or refute suspicion of allergy plan or reinforce management strategy arrange specialist testing (e.g. drug allergy, challenge testing) arrange appropriate specialist support services (e.g. dietician) Some specialised clinics offer desensitisation immunotherapy (see specific guidelines), which can cure or substantially relieve severe allergic rhinitis and insect venom allergies (see references). Authorised by Julia Forsyth Page 4 of 5

5 Who can I discuss patients with or refer to? There are currently no dedicated specialised adult allergy services at Derby (although these are under development). Dr Jennie Gane (Consultant Respiratory Physician) has an interest in allergy and can see referrals for respiratory allergy. A network arrangement with West Midlands Allergy Centre at Birmingham Heartlands and Good Hope Hospitals facilitates review and management of complex allergy referrals. Dr Jennie Gane: Telephone ext [email protected] Specialised Allergy services are also available at Queen s Medical Centre, Nottingham (Dr G Gnanakumaran). Consultant Immunologist (Derby Immunology Laboratory and Birmingham Heartlands Hospital) Dr Aarnoud Huissoon [email protected] (Thursdays) (other days) (Elsa Taylor, PA) For Paediatric Allergy: See separate shared care guideline. References Emergency treatment of anaphylactic reactions 2008 Guidelines for healthcare providers Resuscitation Council (UK) Anaphylaxis: assessment and referral NICE guidance Bee and Wasp sting allergy NICE immunotherapy guidelines UK Allergy Guidelines from BSACI (including venom allergy, urticaria, rhinitis, drug allergy) Authors: Dr Aarnoud Huissoon, Ms Ravina Hira, Jan 2011 Reviewed by: Date: Expiry date: Dr A Huissoon, Dr P Blackwell, Mrs H Seddon April th April 2015 Dr A Huissoon, Dr P Blackwell, Mrs H Seddon Oct st Oct 2017 Authorised by Julia Forsyth Page 5 of 5