Benefits of allergy testing are:
- Knowing exactly what allergens you are allergic to.
- You will have a prevention plan.
- You will have an action plan.
Side effects of allergy testing:
- There could be localised itching.
- Reaction to allergen.
- Localised swelling.
- Anaphylaxis can occur on rare occasions.
- For blood tests there will be a slight bleeding and a needle mark, on rare occasions people might feel faint during the blood test.
Test might not available if the patient has:
- Unstable asthma
- Pregnant (due to potential anaphylaxis)
- Small children/babies due to attention/co-operation
- Medications that cannot be stopped that interfere with the results, and if patient on beta-blockers (as will interfere with effect of adrenaline).
Always inform the consultant about health conditions you have, as these can reduce the test reactivity.
When seeing a consultant ask for an action/allergy plan, this should be always kept with you with your adrenaline auto-injector. This plan is for your understanding how to treat a reaction, but also for other people who might have to administer medication/ adrenaline auto-injector.
If you are happy with your results or you did not get the information you required, you can ask for a second opinion.
While you are with your consultant, keep these questions in mind to ask.
- How should I handle having a food allergy reaction in the future?
- Are food allergies inherited?
- If I need help do I contact the consultant or my doctor?
- What foods am I being tested for and why?
- What do the allergy test results mean?
- How serious could my symptoms be?
- What food allergy management tools are available?
- How can we determine the best way to manage this food allergy?
- Could these allergies improve or worsen with time?
Challenge testing – Oral Food Challenge (adult and child)
If test results of the skin and blood tests are unclear a consultant might a food challenge, or if the patient has not had a reaction in a long time.
This method is giving the patient small amount of food that has suspected allergen in, to see if there is a reaction. This must be done under medical supervision, and never tried at home. You will be asked to bring foods from home, allow different foods for each category in case your child refuses to eat a food at testing, there will be instructions how to do this. It may be also helpful to bring either favourite pack lunchbox, or cutlery from home, to make your child feel more at ease.
If an allergic reaction occurs the consultant might stop the testing depending on the severity. If a mild reaction occurs the consultant may observe and continue.
If the person taking the test is ill on the day, postpone, as the reaction could be greater.
If you did not react to foods, then you may be instructed to start including those foods in your diet, and your consultant will direct you how this will be reintroduced into your diet. If you reacted to the foods, then you will be advised to avoid those foods.
Things to think about:
- Make a list of questions that you want to ask.
- If need to stop antihistamines
- Speak to your child, discuss about it is ok to fail a food challenge. A child can get down like adults, instil positivity, confidence.
- Does your child have any questions?
- Although its will be a long day, and depending on how feeling after testing, maybe doing something fun after the testing would be good.
- Eating beforehand -you may be asked to avoid food, or have a light meal, if this information not available phone, speak to the consultant secretary.
This test can take between 3-6 hours, so be prepared for the day, things to take with you:
- Change of clothing, in case of vomiting, and a bag to put dirty clothes in.
- Activities for either distraction or relieve boredom.
- Take all medication, including Adrenaline Auto-Injectors.
- Water, for staying hydrated, if vomited, so on – water is best option so does not affect the results of the testing.
- Food for after testing, safe snacks because length of testing and hungry.
Skin prick testing (SPT)
This can be done from 6 moths and older, you cannot have this if you are pregnant or have Dermographism (common form of physical or chronic inducible urticaria).
Before testing if you are on antihistamines, you will be asked to stop them 3-5 days prior testing. No steroids to be taken 5-10 prior to test. Always be guided by literature given to you or the advice from your consultant/doctor.
Drops of liquid is placed on the forearm, which contains allergens, this method can test up to 25 allergens in one go. The skin where the liquid is placed on the arm is softly pricked. The results are if you are allergic to the allergen placed on your arm, it will become itchy and maybe small hive will be present, this is normally 15 minutes after the allergen placed on your arm.
The reaction is measured, the larger the reaction is the person is truly allergic rather than sensitive. Sometimes the results might not be accurate, as false positives and false negatives can occur, also it cannot predict the severity of an allergic reaction.
False readings for reactions can be given because food is place on skin and not digested as normally. Also, some foods have similar protein, test might show you have a green bean reaction when you have not had a problem before, this is because the green bean is the same food family as peanuts (legumes) this is known as cross-reactivity. The test is positive because it recognises a similar protein in peanuts and green beans, but the test has not detected the real reason—another, different protein that is found only in peanuts.
This test will be used with other information given to give a diagnosis. You may be asked to bring foods from home for testing, if this is required you will be asked to keep foods in separate sealed food bags or separate containers, to stop cross contamination. The testing takes 15 minutes, but consultation can take up to 45 minutes. Test is avoided if have widespread eczema, taking antihistamines or steroids, in this case blood testing might be done.
You might have localised itching, it normally settles within 45 minutes, washing the area in cold water may be helpful, if concerned or worse reaction see medical advice.
A welt over 3mm will be deemed as a positive reaction and under 3mm is a negative reaction.
Suspected foods will be asked to be removed from your diet for a few weeks. Then with medical advice you are asked to reintroduce the food back into your diet to see if reaction reoccurs. Foods elimination, and reintroduction should only be done with medical advice. Long term unsupervised restricted diets should not be undertaken, as this can lead to malnutrition.
Bloods are taken and analysed; this is done by seeing how your body’s immune system respond to the allergen. Your immune system reacts by making antibodies called IgE. (immunoglobulin E) specific to that allergen. Your blood sample is mixed with that allergen, then the blood is measured for the level of IgE in the sample. Blood tests are not always accurate, as some people can be allergic to an allergen, but it does not show up in the IgE, this is because the allergen may not be present in your system when the blood test is taken. Another reason the test can show a false result, if looking for peanut allergy, and the patient ate legumes recently e.g., green beans the same protein would be found in the bloodstream.
This test will be used with other information given to give a diagnosis. The blood test only takes a few minutes, and the results can be back in 2-3 days.
Allergies are split into 2 categories.
- Immediate type (IgE mediated) reactions – this is where the release of chemicals from mast cells have burst.
- Delayed type (non-IgE mediated) reactions – this is where it takes longer to escalate, causing swelling and damage (inflammation) to the body parts that have reacted.
You can eat and drink as normally, but it is always advisable to get advice from your consultant/doctor first. If a child is having the blood test maybe bring a favourite toy/teddy to give them slight distraction, and comfort. Adults and children have blood tests in their arms, babies will have the blood test taken from the heel of their foot with a heel stick that collects a tiny amount of blood for testing. A heel stick is a small needle or a lancet. If a child is having a blood test or heel stick the parent can stay with the child while the process is being performed.
Allergens (smallest amount possible) are added to metal discs or a small amount if allergen direct onto bandage, then they are taped to your body for 48 hours or maybe longer. If you are allergic to the allergen, then you will have a localised rash. This type of test is used to identify type of eczema known as Contact Dermatitis.
An example of Questionnaire for patch testing.
- Were you told enough information on how patch testing works? Was written information supplied?
- Did you react to the patch test?
- How long did it take for you to react?
- Did you take any antihistamines during the 48 hours of patch testing? (suppressed immune system)
- Did you spend any time out in the sun? (may dampen the skin’s immune system.)
- Did you suffer any side effects?
- Did you shower or bathe during the patch testing?
- Did you exercise during the patch testing?
- Did the patch test come off, and if so, what did you do? E.g., left it off or reapplied.
- How did the patch test affect you? e.g., symptoms?
- Were your results explained to you sufficiently?
- What have you learnt from the patch testing? Has the patch testing supplied information about allergens you are allergic to? What are you allergic to?
- Would you recommend patch testing to someone else? Please explain your answer why?
- Is there anything else you would like to add about your experience of patch testing?
Allergy testing kits
These kits are not recommended as they can be unreliable or not the quality of testing provided by NHS or private clinics. Also tests results should be interpreted by a medical professional, especially a medical professional who knows your medical history. These tests are expensive, and sometimes wrong allergens list allergic to is given, resulting in either risk to health or poor nutrition.
Home test kits for coeliac disease, this are done by pricking finger for blood. If the test comes back positive, you need to speak to a doctor as this is not a final result, as a gut biopsy is needed. Also, the NHS does this testing for free.
Home testing kit for allergies, some companies claim they can do these tests from a sample of hair, or your grip strength. Either of these home testing its hold no scientific value.
If you have purchased a home allergy test kit, and the results have come back, please speak to a doctor/consultant/nutritionist before eliminating foods as eliminating foods could cause dietary/ nutritional problems.
Anaphylaxis: assessment and referral after emergency treatment Nice Guidelines
These lists are guidance only, and not fully extensive, people are advised that it is the responsibility of the individual when using this information.
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