Allergies - Diagnosis 

Diagnosing an allergy 

A skin prick test is the first test your doctor will suggest if they suspect an allergy 

If you think you have an allergy, tell your GP about the symptoms you are having, when they happen, how often they occur and if anything seems to trigger them.

Your GP will also want to know if any family members have similar symptoms, or if there is a family history of allergy.

After asking about your allergy history, your GP may carry out tests to identify the allergen that is causing your symptoms, or refer you to a specialist at an allergy clinic. There are NHS allergy clinics across the UK, so you shouldn't have to travel far.

Even if you think you know what's causing the allergic reaction, you may need to be tested to determine the exact allergen and get a definite diagnosis.

The type of test you are offered will depend on your symptoms, the condition of your skin and any medication you are taking. Possible tests include:

  • Skin prick test. This is usually the first test to be done when looking for an allergen. The skin is pricked with a tiny amount of the suspected allergen to see if there is a reaction. If there is, the skin around the prick will very quickly become itchy, red and swollen. Because the skin prick test introduces such a tiny amount of allergen into the skin, the testing is considered very safe and can be used on almost any age group, including babies. However, it may not be suitable if you have severe eczema or if you are taking antihistamines.
  • Blood test. This is used to measure the amount of IgE antibodies in your blood that have been produced by your immune system in response to a suspected allergen. The results are given on a scale from zero to six: zero indicates a negative result and six indicates an extremely high sensitivity. Blood tests are particularly useful when you are at risk of an extreme reaction or when a rare allergen is suspected.
  • Patch test. This test is used to find an allergen causing eczema (contact dermatitis). A small amount of the suspected allergen is added to special metal discs, which are then taped to your skin for 48 hours and monitored for a reaction. This test is usually carried out at a dermatology (skin) department in a hospital.

The use of commercial allergy-testing kits is not recommended. These tests are often of a lower standard than those provided by the NHS or accredited private clinics. Also, allergy tests should be interpreted by a qualified professional who has detailed knowledge of your symptoms and medical history.

Page last reviewed: 23/03/2012

Next review due: 23/03/2014

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Allergy testing

If you think you have an allergy, here's advice on how to get diagnosed with NHS-approved allergy tests