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    Allergy testing

    On this page
    1. What is an allergy test?
    2. Can I have a test for lactose intolerance?
    3. Can I have a test for wheat intolerance?
    4. How do I know if I need an allergy test?
    5. Where can I get an allergy test?
    6. Get treated for allergies with Online Doctor

    Allergy test

    Allergies are caused by your immune system responding to certain substances as though they are harmful. This type of immune response – an allergic reaction – creates unpleasant symptoms including sneezing, coughing, wheezing, and rashes.

    Allergies are increasingly common across the world. According to the NHS, more than one in four Brits are affected by allergies at some point in their life. Although allergies are more common in children, many adults are also affected – and it’s possible to develop new allergies as you get older.

    If you’re concerned that you or your child might have developed a new allergy, it’s important to talk to your GP. They can offer advice about managing symptoms and, if necessary, refer you for testing at an allergy clinic

    What is an allergy test?

    There are a few different types of allergy test, but the basic idea is to work out what’s causing your allergy and how severe it is. The tests will be designed to look for different types of allergy which affect the body in different ways, according to the symptoms you’ve been having.

    • Skin prick tests are where a drop of liquid containing an allergen is placed on the skin. The same area of skin is then gently pricked with a needle. If you have an allergy to that particular substance, an itchy red bump will appear where your skin was pricked within about 15 minutes.
    • Patch tests are commonly used to diagnose contact dermatitis (eczema that is brought on by contact with certain allergens). With a patch test, a small amount of the suspected allergen is put onto a metal disc which is then taped to your skin for 48 hours.
    • Blood tests can be used to check whether your body has created antibodies in response to specific allergens.
    • Elimination diets are used to find food allergies. Certain foods are removed from your diet one by one, then gradually reintroduced.
    • Challenge testing is also used to find food allergies. This is a supervised test where you eat increasing amounts of the suspected allergen. You have to do this under strict supervision, as medical staff need to be present in case of a severe reaction.

    Can I have a test for lactose intolerance?

    Yes, but a food intolerance is not the same as an allergy, so the tests are completely different.

    In people with allergies, the immune system interprets normal substances as harmful and releases attacking chemicals like histamine. In people with food intolerances, the body simply has trouble digesting a specific substance.

    In the case of lactose intolerance, the issue is normally a lack of lactase. This is an enzyme that helps your body to break down lactose (a sugar found in dairy products). Rather than being broken down into glucose and galactose in the small intestine, the lactose is broken down in the colon. This process releases acids and gases that cause bloating, flatulence, and diarrhoea.

    A test for lactose intolerance may not be needed – your GP may simply advise that you cut dairy from your diet for a couple of weeks to see if your symptoms improve. Sometimes they may want to do some tests to check:

    • how much hydrogen is in your breath – people with lactose intolerance produce more hydrogen than normal
    • your blood glucose levels after drinking milk or a lactose solution – your glucose levels will not be affected, or will rise very slowly, if you have lactose intolerance

    Your GP may want to do different tests if they suspect that something else is causing your symptoms. Conditions like irritable bowel syndrome (IBS) can cause similar symptoms, as can an intolerance to the protein in cows’ milk.

    Can I have a test for wheat intolerance?

    There is currently no diagnostic test for wheat intolerance, so the best way to find out if you have an intolerance is to try cutting out wheat products from your diet.

    It may be that the cause of your symptoms is coeliac disease. This is an autoimmune disease triggered by eating gluten that can cause diarrhoea, stomach aches, bloating, flatulence, indigestion, and constipation, as well as tiredness and weight loss. The test for coeliac disease normally involves having a blood test, followed by a biopsy.

    How do I know if I need an allergy test?

    You might need allergy tests if your symptoms are very severe and/or it’s not clear what you’re allergic to. The good news is: getting tested isn’t something you have to decide on yourself – your GP will decide whether you need testing or specialist help at an allergy clinic.

    Where can I get an allergy test?

    If your GP provides a referral, you can get tested at a specialist NHS allergy clinic. You can also get tested at a private clinic, and pay for your own allergy tests.

    It’s not recommended that you use an at-home allergy testing kit if you suspect you have an allergy. These are considered to be of a low standard and generally unreliable.

    Get treated for allergies with Online Doctor

    If you’ve been diagnosed with allergies and you’re seeking easy, efficient treatment, visit our allergy clinic. Our in-house clinicians can prescribe antihistamines for hay fever.


    Authors and editors

    • Written by

      Dr Sameer Sanghvi
      GMC number: 7085078
      Date published: 14th April 2021

    • Reviewed and updated

      Dr Jean Wong
      GMC number: 6132403
      Date reviewed: 2nd October 2023

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