Allergy Blood Tests in London: Can IgE Identify Hay Fever Triggers?

?Written by: London Blood Tests Editorial Team

Published: 31st of July 2026

Repeated sneezing, itchy eyes and a blocked or runny nose can make spring and summer difficult. Yet pollen is not the only possible explanation. House dust mites, animal dander and moulds can cause similar symptoms throughout the year.

An allergy blood test can measure allergen-specific IgE antibodies to pollens and other environmental substances. This may help identify allergens to which your immune system has become sensitised.

However, a positive result does not automatically prove that an allergen is causing your symptoms. Test results must be interpreted alongside when symptoms occur, where they occur and what you were exposed to at the time.

Allergy blood testing at a glance

• Hay fever specifically refers to an allergic reaction to pollen.

• House dust mites, pets and indoor moulds more commonly cause perennial or environmental allergic rhinitis.

• An IgE blood test can measure antibodies to individual allergens.

• Specific IgE indicates sensitisation, not necessarily clinical allergy.

• Total IgE cannot identify a particular trigger and is not diagnostic on its own.

• Targeted testing is often more useful than testing hundreds of unrelated allergens.

• Antihistamines generally do not need to be stopped before an IgE blood test.

• Allergy blood testing can be performed outside the pollen season.

• Results cannot reliably predict how severe a future reaction will be.

NHS laboratory guidance emphasises that specific IgE testing should be chosen and interpreted according to the person’s clinical history. A positive result without a matching pattern of symptoms may have limited clinical significance. (Oxford University Hospitals: Allergen-specific IgE antibodies)

What is hay fever?

Hay fever, also called seasonal allergic rhinitis, is an allergic reaction to pollen.

Common symptoms include:

• Sneezing

• A blocked or runny nose

• Itchy, red or watery eyes

• An itchy nose, throat, mouth or ears

• Coughing

• Headaches

• Reduced sense of smell

• Tiredness

Symptoms are commonly worse between late March and September, although the precise period depends on the pollen involved and the weather. Warm, humid and windy conditions can increase pollen exposure. (NHS: Hay fever)

Different plants release pollen at different times:

• Tree pollen is often more prominent during spring.

• Grass pollen commonly causes symptoms during late spring and summer.

• Weed pollen may contribute later in the season.

A person whose symptoms peak in April may therefore have a different trigger from someone who becomes unwell every June.

Hay fever versus perennial allergic rhinitis

Hay fever specifically concerns pollen. Similar nasal and eye symptoms can be caused by allergens present throughout the year.

Someone whose symptoms worsen mainly outdoors during the summer may benefit from pollen-focused testing. Someone who wakes with a blocked nose throughout the year may need indoor allergens considered.

How does an IgE allergy blood test work?

Immunoglobulin E, usually shortened to IgE, is an antibody involved in immediate allergic reactions.

An IgE blood test can assess:

• Total IgE

• Specific IgE to an individual allergen

• Groups of related allergens

• Individual allergen proteins in some advanced panels

If specific IgE is detected, the immune system has become sensitised to that substance.

Sensitisation does not necessarily mean that the person develops symptoms when exposed. Some people have detectable IgE antibodies but tolerate the allergen without difficulty.

The reverse also requires caution. A negative test does not always provide a complete explanation for persistent symptoms. The clinical history remains central to diagnosis.

What is the difference between total IgE and specific IgE?

Total IgE

Total IgE measures the overall concentration of IgE antibodies in the blood.

It may be raised in association with:

• Allergic conditions

• Atopic eczema

• Allergic asthma

• Parasitic infections

• Certain uncommon immune disorders

Total IgE cannot identify which allergen is responsible. A raised result does not prove allergy, while a result within the reference interval does not completely exclude sensitisation to a specific substance.

NHS laboratory guidance states that total IgE is not generally useful as a standalone diagnostic test for allergy. (Gloucestershire Hospitals: Total IgE)

Allergen-specific IgE

Specific IgE measures antibodies directed towards a particular allergen, such as:

• Grass pollen

• Birch pollen

• House dust mites

• Cat dander

• Dog dander

• Alternaria mould

Specific testing is most useful when the selected allergens reflect the person’s symptoms and likely exposures.

For example, a grass-pollen result is more meaningful in someone whose symptoms repeatedly worsen during the grass-pollen season than in someone who has no outdoor or seasonal symptoms.

Which environmental triggers can be tested?

Grass pollen

Grass pollen is one of the most frequent causes of hay fever.

Symptoms commonly become more noticeable during late spring and summer and may worsen:

• In parks or gardens

• Near recently cut grass

• During dry, windy weather

• When windows are open during high-pollen periods

Panels may assess individual grass species or a grouped grass-pollen marker.

Tree pollen

Tree pollen commonly causes symptoms earlier in the year.

Depending on the panel, testing may include trees such as:

• Birch

• Alder

• Hazel

• Oak

• Beech

• London plane

A positive result should be compared with the months when symptoms occur and the person’s likely exposure.

Some people sensitised to birch pollen also experience itching or mild swelling in the mouth after eating certain raw fruits or nuts. This may occur because pollen and food proteins can have similar structures.

Weed pollen

Weed pollens may contribute later in the pollen season.

Examples that may be included in testing are:

• Mugwort

• Plantain

• Ragweed

The clinical significance depends on geography, local vegetation and exposure history.

House dust mites

House dust mites are indoor allergens rather than pollen allergens. They may cause symptoms throughout the year.

Commonly tested mite species include:

• Dermatophagoides pteronyssinus

• Dermatophagoides farinae

Symptoms may be more noticeable:

• In bedrooms

• Around carpets and upholstered furniture

• When making the bed

• In warm, humid indoor environments

A positive specific IgE result supports sensitisation but should still be matched with symptoms and exposure.

Animal allergens

Environmental panels may assess allergens associated with:

• Cats

• Dogs

• Horses

• Rabbits

• Guinea pigs

• Hamsters

The allergenic proteins are commonly found in dander, saliva and other secretions—not simply in the animal’s hair.

Animal allergens can remain on clothing, furniture and carpets even when the animal is no longer present.

Moulds and fungal spores

Mould sensitisation may be considered where symptoms occur in damp buildings or environments with visible mould.

Commonly assessed moulds include:

• Alternaria alternata

• Aspergillus fumigatus

• Cladosporium herbarum

• Penicillium species

A positive result requires careful interpretation. Damp environments may also cause irritation or respiratory symptoms through mechanisms that are not IgE-mediated.

Can an allergy blood test diagnose hay fever?

Not by itself.

A diagnosis depends on whether the test result matches a convincing clinical history.

Useful questions include:

• Which symptoms occur?

• During which months are they present?

• Are they worse indoors or outdoors?

• Do they begin after gardening or spending time near grass?

• Are they linked to a pet or a particular building?

• Do symptoms recur under similar circumstances?

• Do they improve away from the suspected environment?

• Have antihistamines or nasal treatments helped?

A positive grass-pollen result is more clinically relevant when symptoms reliably occur during the grass-pollen season. The same result may be incidental in someone without seasonal symptoms.

NHS laboratory services describe clinical history as the foundation of allergy investigation. Specific IgE can support that assessment when the correct allergens have been selected. (Great Ormond Street Hospital: Specific IgE)

What does a positive result mean?

A positive specific IgE result means that antibodies to the tested allergen were detected.

It does not necessarily show:

• That the allergen causes symptoms

• How severe a reaction could be

• That every exposure will trigger a reaction

• That the allergen must be completely avoided

• That the result explains every symptom

Specific IgE results are commonly reported numerically or within laboratory classes. Higher results may increase the likelihood that sensitisation is clinically relevant, but no single value confirms allergy for every person and every allergen.

Testing a large number of unrelated allergens increases the chance of finding positive results that do not match the person’s symptoms.

Targeted or comprehensive testing?

The appropriate approach depends on the complexity of the symptoms.

Testing almost 300 allergens is not routinely necessary for straightforward seasonal hay fever.

Broad multiplex testing may be more appropriate where:

• Symptoms are complex

• Several different allergy types are suspected

• Previous targeted testing has not clarified the cause

• Cross-reactivity needs specialist assessment

• A healthcare professional has recommended a comprehensive panel

The British Society for Allergy and Clinical Immunology notes that component-resolved and multiplex tests may provide useful information in complex cases, but testing many allergen components can generate results that are difficult to interpret. (BSACI: Component-resolved diagnosis)

What are molecular allergens?

Traditional allergy testing may assess an extract from an entire allergen source. Molecular or component-resolved testing examines specific proteins within that source.

This can sometimes help distinguish:

• Primary sensitisation

• Cross-reactivity between related pollens

• Reactions associated with similar proteins

• Complex sensitisation patterns

For example, sensitisation to a birch-pollen protein may be associated with oral symptoms after eating certain raw plant foods because the proteins are structurally similar.

Molecular results remain specialist information. They cannot independently predict the severity of a future reaction and should not be used alone to justify extensive avoidance.

Is blood testing better than skin-prick testing?

Neither method is universally superior.

Blood testing may be considered when:

• Antihistamines cannot easily be stopped

• Extensive eczema makes skin testing difficult

• Skin testing is not readily available

• The patient has a history that makes direct testing less suitable

• A venous sample is preferred

Skin-prick testing may provide rapid results and can be useful when performed and interpreted by appropriately trained professionals.

The choice should be based on the person’s clinical history and circumstances rather than the total number of allergens available.

Do you need to stop antihistamines?

Antihistamines generally do not need to be stopped before an allergy blood test.

These medicines can reduce the skin response during skin-prick testing, but they do not prevent the laboratory from measuring circulating allergen-specific IgE.

Tell the provider about:

• Antihistamine tablets

• Nasal sprays

• Asthma medication

• Steroid treatment

• Adrenaline auto-injectors

• Previous severe reactions

• Pregnancy

• Other prescribed medicines

Do not stop medicines required to control asthma or prevent serious reactions without medical advice.

Do you need to fast?

Fasting is not normally required for total IgE or allergen-specific IgE testing when these are the only markers being assessed.

Follow the preparation instructions for the exact panel because requirements may differ if unrelated blood markers are included.

Can you test outside the hay-fever season?

Yes.

Specific IgE antibodies can be measured even when the person is not currently experiencing symptoms.

Testing outside the season may be convenient when preparing for the following spring or summer. The person should still provide information about:

• The months when symptoms usually occur

• Whether symptoms peak outdoors

• Suspected pollen exposure

• Medication used during the season

• Whether the pattern returns each year

A result collected in winter can still be relevant to a consistent history of summer hay fever.

Which London Blood Tests allergy panel may be suitable?

The panel should be selected according to the symptoms—not simply according to the largest number displayed in the product name.

Extended Allergy Panel

The Extended Allergy Panel includes allergen-specific IgE testing across environmental and food allergen groups.

Its environmental markers include:

• Grass, tree and weed pollens

• House dust mites

• Cat and dog allergens

• Other animal allergens

• Moulds and fungi

This may be suitable where seasonal and year-round environmental symptoms overlap.

Before booking, check the current biomarker list to confirm that the suspected trigger is included.

Allergy Complete – 295 Allergens Tested

The Allergy Complete – 295 Allergens Tested is a broad multiplex panel covering environmental allergens, foods, insect venoms and molecular allergen components.

It may be considered where:

• The symptom history is complex

• Several allergen groups are suspected

• Both seasonal and indoor reactions occur

• Cross-reactivity requires assessment

• Targeted testing has not provided a clear explanation

This degree of testing is not routinely necessary for uncomplicated hay fever. The results may identify sensitisation that has no relationship to the patient’s symptoms.

Broad panel results should ideally be interpreted by a clinician with appropriate allergy knowledge.

Where can you arrange an allergy blood test in London?

Private allergy blood testing is available through London Blood Tests partner clinics in:

• Knightsbridge: Astrum Medical, 43 Cheval Place, SW7 1EW

• Holborn: GB MedLabs, 1 Portpool Lane, EC1N 7UU

• Paddington: Dr Ducu Clinics, 199 Gloucester Terrace, W2 6LD

• Gants Hill: Olive Health, 23A Seven Ways Parade, IG2 6JX

Home and hotel blood collection can also be arranged. Appointment availability, collection fees and turnaround times should be confirmed when booking.

London Blood Tests lists its contact number as 0203 488 0809. (London Blood Tests: About us)

When comparing a private allergy test in London, ask:

• Does the panel include the pollen or environmental allergens relevant to my symptoms?

• Does it measure allergen-specific IgE?

• Is total IgE also included?

• Is the panel targeted or multiplex?

• Is professional interpretation available?

• How long will the results take?

• Is a venous sample required?

• What follow-up is available if a result is positive?

A targeted panel that matches the history may provide more useful information than a much larger panel containing unrelated allergens.

What should you do with the results?

Review the results against what actually happens when you are exposed.

Consider:

• Was the allergen present when symptoms occurred?

• Does the result match the season?

• Do symptoms recur in the same environment?

• Is the result strongly or weakly positive?

• Are there other possible explanations?

• Could the result reflect cross-reactivity?

• Does the reaction pattern require specialist assessment?

A clinically relevant result may support:

• Reducing exposure where practical

• Planning hay-fever medication before the season begins

• Reviewing asthma symptoms

• Discussing nasal sprays or antihistamines with a pharmacist or clinician

• Seeking specialist allergy advice

• Considering allergen immunotherapy where clinically appropriate

Do not make major dietary or lifestyle restrictions solely because of an isolated blood result.

When should you seek urgent help?

Call 999 if an allergic reaction causes:

• Sudden swelling of the mouth, lips, tongue or throat

• Difficulty breathing

• Severe wheezing

• A tight throat or difficulty swallowing

• Collapse, fainting or sudden confusion

• Blue, grey or very pale lips or skin

These may be signs of anaphylaxis. Use an adrenaline auto-injector immediately if one has been prescribed and follow the emergency plan provided by your clinician. (NHS: Allergies)

Frequently asked questions

Can an allergy blood test confirm hay fever?

It can support the diagnosis by identifying specific IgE sensitisation to pollen. A matching history of seasonal symptoms is still required.

What is the difference between hay fever and environmental allergy?

Hay fever specifically refers to pollen allergy. House dust mites, animals and indoor moulds can cause similar symptoms but are more commonly associated with perennial environmental allergic rhinitis.

What is the difference between total IgE and specific IgE?

Total IgE measures the overall concentration of IgE antibodies. Specific IgE measures antibodies directed towards an individual allergen, such as grass pollen or house dust mites.

Does a positive result mean I have an allergy?

Not necessarily. A positive result shows sensitisation. It becomes more clinically meaningful when it matches a consistent pattern of symptoms after exposure.

Can antihistamines affect an IgE blood test?

Antihistamines generally do not interfere with laboratory measurement of specific IgE. They may affect skin-prick testing.

Do I need to fast?

Fasting is not normally required for standard total or specific IgE testing.

Can testing be performed during winter?

Yes. Specific IgE can be measured outside the pollen season, although the result must still be compared with the person’s usual seasonal symptoms.

Is a 295-allergen panel better than targeted testing?

Not necessarily. Broad testing may be useful in complex cases but can also produce positive results unrelated to the patient’s symptoms. Targeted testing is often more informative for straightforward hay fever.

Book a private allergy blood test in London

London Blood Tests offers environmental allergy panels through London clinics and home or hotel collection.

An allergy blood test may help identify sensitisation to pollens, house dust mites, moulds and animal allergens. Its value depends on selecting allergens that match the person’s symptoms and interpreting the results within the clinical history.

Choose the smallest panel that adequately addresses your suspected triggers. A greater number of allergens does not automatically provide a clearer diagnosis.

References

1. NHS: Hay fever

2. NHS: Allergies

3. Oxford University Hospitals: Allergen-specific IgE antibodies

4. Oxford University Hospitals: Total IgE

5. Great Ormond Street Hospital: Specific IgE

6. Royal Brompton and Harefield Hospitals: Specific IgE blood test

7. BSACI: Component-resolved diagnosis

Medical disclaimer: This article provides general information and does not replace individual medical advice, diagnosis or treatment. Seek medical assessment for persistent allergy symptoms, asthma, suspected severe allergy or any history of anaphylaxis.