Allergy blood test or skin prick test: which is right for you?
Short answer: a skin prick test and an allergy blood test both look for IgE, the antibody behind hay fever, food allergies and most allergic reactions. A skin prick test gives results within about 20 minutes but is usually done in an allergy clinic and needs you to stop antihistamines first. A blood test needs one sample, is not affected by antihistamines or skin conditions, and can check hundreds of allergens at once. Neither test diagnoses an allergy on its own; results always need to be read alongside your symptoms.
How a skin prick test works
A drop of each allergen is placed on your forearm and the skin is gently pricked. If you are sensitised, a small itchy bump appears within 15 to 20 minutes. It is quick and widely used in specialist allergy clinics, but only a limited number of allergens are tested in one sitting.
Skin prick testing is not suitable for everyone. Antihistamines need to be stopped for several days beforehand, and it can be hard to read on skin affected by widespread eczema or conditions that make the skin react to scratching.
How an allergy blood test works
A small blood sample is sent to a laboratory, which measures IgE antibodies to specific allergens. There is no need to stop antihistamines, skin conditions do not affect the result, and there is no exposure to the allergen itself.
Modern molecular blood tests go further. They measure IgE to the individual proteins inside an allergen, which helps show whether a reaction is likely to be to the allergen itself or a cross-reaction. For example, some people with birch pollen allergy get an itchy mouth from apples because the proteins are similar, which is usually milder than a true food allergy.
Side by side
Speed: skin prick results in about 20 minutes; blood test results in a few working days.
Antihistamines: must be stopped before a skin prick test; no need to stop them for a blood test.
Eczema and skin conditions: can make skin testing hard to read; blood tests are unaffected.
Number of allergens: usually a small panel for skin testing; a single blood sample can check around 300 allergens.
Where: skin prick testing is usually done in an allergy clinic; blood can be taken at a local clinic.
What the results can and cannot tell you
A positive result shows sensitisation, meaning your immune system has made IgE to that allergen. It does not always mean you will react to it. Many people are sensitised to foods they eat without any problem. That is why results are interpreted alongside your history, and why specialists sometimes use a supervised food challenge to confirm a food allergy.
Neither test is designed to diagnose food intolerance, such as lactose intolerance, which does not involve IgE.
Which test should you choose?
A blood test is often the practical first step if you take antihistamines every day, have eczema, want to check many possible triggers at once, or cannot easily get a specialist appointment. If you have had a severe reaction, or your results are unclear, a referral to an allergy specialist is the right next step, and your blood test results can help that conversation.
Our Advanced Allergy Blood Test checks around 300 allergens, including pollens, foods, nuts, pets, dust mites, moulds and insect venoms, from one blood sample. It costs £399 all-inclusive, with a clinician-reviewed report and results in 2-5 working days.
When to see a doctor
Call 999 if you or someone else has swelling of the lips, tongue or throat, difficulty breathing, or feels faint after contact with a possible allergen. See your GP if you have reactions you cannot explain, symptoms that affect your sleep or daily life, or you are unsure whether you need an adrenaline auto-injector.
Frequently asked questions
Is an allergy blood test as accurate as a skin prick test?
Both are well established and look for the same antibody. Each can show sensitisation that does not cause symptoms, so both are interpreted alongside your history.
Do I need to stop antihistamines before an allergy blood test?
No. Antihistamines do not affect an allergy blood test.
Can children have an allergy blood test?
Yes. At Easy Medical Centre, children aged 4 and over can be tested at our Crewe clinic. Our other clinics see adults only.
Does an allergy test show food intolerances?
No. Allergy tests look for IgE-mediated allergy. Food intolerances work differently and are not diagnosed this way.
Sources
NICE clinical guideline CG116: Food allergy in under 19s, assessment and diagnosis
NHS: Allergies, diagnosis
British Society for Allergy and Clinical Immunology (BSACI) patient information on allergy testing
Related reading
This article is general information based on UK guidance. It is not personal medical advice. If you are worried about your health or have symptoms, speak to your GP or call 111. If you have signs of a severe allergic reaction, such as swelling of the lips or tongue or difficulty breathing, call 999.
