Allergy Blood Tests UK: Can a Blood Test Detect Allergies?
If you have ever sneezed through summer, broken out in hives after a meal, or spent a winter unable to shift a blocked nose, you have probably wondered what is causing it. Allergies affect roughly one in four people in the UK at some point, and they range from mildly annoying to genuinely serious.
The two main ways to test for allergies are a skin prick test, usually done at a clinic, or a blood test. This article is about the blood option.
What an allergy blood test measures
An allergy blood test looks for immunoglobulin E (IgE) antibodies in your blood. These are the molecules your immune system makes when it decides a harmless substance is a threat. When you encounter something you are allergic to, your body releases IgE and that triggers the release of histamine, which is what gives you the symptoms.
There are two types of IgE test:
Total IgE measures the overall amount of IgE circulating in your blood. A high level can suggest an allergic tendency, but it does not tell you what you are allergic to.
Specific IgE (sometimes called RAST or ImmunoCAP) measures IgE directed against a particular substance: grass pollen, peanuts, cat dander, house dust mite, and so on. This is the test that gives you a usable answer.
A specific IgE test can be ordered as a single allergen check or as a panel covering the most common triggers in the UK: grass and tree pollen, moulds, dust mites, pet proteins, and key foods like milk, egg, peanut, and shellfish.
Blood test vs skin prick test
Skin prick testing is still the standard first-line approach in the NHS. A small drop of allergen extract is placed on your forearm and pricked into the skin. If you react, a raised wheal appears within about 15 minutes.
Blood testing has some advantages:
You do not need to stop antihistamines. Skin tests require you to come off antihistamines for up to a week. Having tried that during hay fever season, I would not recommend it unless you have to. Blood tests do not have this problem.
It is safer if you have had a severe reaction. If you have a history of anaphylaxis, putting the allergen into your skin carries some risk. A blood test avoids direct exposure.
It works regardless of skin conditions. Eczema, psoriasis, or dermatographism can make skin testing unreliable. Blood tests bypass the skin entirely.
One sample can test many allergens. A single blood draw can be checked against a panel of dozens of allergens without needing multiple skin pricks.
The downside is that blood tests cost more and the results take days rather than minutes. If you need answers on the spot, a skin test at an allergy clinic is faster.
Is it worth paying privately?
The NHS does offer allergy testing, but referral thresholds are high. NICE recommends NHS allergy testing when symptoms are severe, poorly controlled, or accompanied by other risk factors like asthma. Mild or occasional symptoms often do not meet the criteria, and waiting lists can be long.
Private blood testing gives you control. You choose which allergens to test for, you do not need a GP referral, and you get results in a few days.
To compare individual tests, you can look at IgE or allergy blood tests side by side.
Private allergy blood test costs in the UK
Prices change, so check the live product page before ordering. These were the prices during our research:
| Provider | Test | Price | Link |
|---|---|---|---|
| Medichecks | IgE (Immunoglobulin E) Blood Test | £60 | View test£60 |
| Medichecks | Immunoglobulins IgG/IgM/IgA Blood Test | £99 | View test£99 |
| Forth | Immune System Blood Test | £98 | View test£98 |
Medichecks offers the most affordable standalone IgE test at £60. Forth’s Immune System test is a broader panel that goes beyond allergy markers and includes white blood cell subtypes and immunoglobulins.
A private allergy blood test is a useful starting point, but it does not replace a clinical assessment. If your specific IgE result is positive, you still need a GP or allergist to interpret what that means in the context of your symptoms.
What a positive result actually means
A positive specific IgE result tells you that your body has made antibodies to that substance. It does not tell you how severe your reaction will be. Some people have high IgE to peanuts and tolerate them without symptoms. Others have low IgE and get hives from a single bite.
This is why allergy testing is never just about the numbers. A positive test plus a clear history of symptoms after exposure is what makes the diagnosis. If your test is positive but you have never reacted to that food or pollen before, you may have sensitisation rather than a clinical allergy. The distinction matters because sensitisation alone does not require treatment.
What if your results are normal?
A normal total IgE and a negative specific IgE panel makes a classical IgE-mediated allergy unlikely. That is useful information, but it does not rule out every allergic or intolerance condition.
Some people have non-IgE mediated food allergies, such as food protein-induced enterocolitis syndrome (FPIES), which does not show up on standard allergy blood tests. Food intolerances like lactose or histamine intolerance are not allergies and will not appear on an IgE test either.
If your symptoms keep coming back despite negative allergy blood work, keep looking. Mast cell disorders, autoimmune conditions, and chronic sinusitis can all produce allergy-like symptoms.
When Not to Test
An allergy blood test cannot diagnose a food allergy on its own. A positive specific IgE shows sensitisation, so if you have never reacted to that food the result can lead to avoidance you do not need, and a diagnosis needs a positive test alongside a clear history of symptoms after exposure. IgE testing also misses non-IgE mediated food allergies such as FPIES, and intolerances like lactose will never appear on it. If you have had a severe reaction such as anaphylaxis, throat swelling or difficulty breathing, that is an emergency, not a reason to order a test first.
Header image from Pexels
Disclaimer: This article is for informational purposes only and is not a substitute for professional medical advice. Always consult a GP or qualified healthcare provider before making decisions about your health.