Allergen Testing in ENT: Skin-Prick Test and Specific IgE
Allergen testing helps identify whether a patient has immune sensitisation to a selected allergen that may be relevant to symptoms such as allergic rhinitis or allergic conjunctivitis. A positive result alone does not prove that exposure causes illness. The test must fit the patient’s history, examination and likely exposure. In ENT practice, testing is most useful when the result will clarify the diagnosis or change counselling and management.
Learning outcomes: Take a focused allergy history before requesting tests; distinguish sensitisation from clinical allergy; compare skin-prick testing with serum allergen-specific IgE; describe the principles and safety limits of skin testing; interpret positive, negative and discordant results; and recognise inappropriate testing.
Clinical safety: These notes support revision and supervised learning. Skin testing should be selected, performed and interpreted by appropriately trained staff using the facility’s protocol and validated reagents. Do not tell a patient to stop prescribed medicines without advice from the clinician or testing service. A patient with breathing difficulty, facial or tongue swelling, collapse, or rapidly progressive symptoms needs emergency care, not diagnostic testing.
What an allergen test can—and cannot—show
In an IgE-mediated allergic response, immunoglobulin E (IgE) directed against a particular allergen can trigger mediator release after exposure. In the upper airway this may produce sneezing, itching, watery nasal discharge, congestion and itchy or watery eyes. A skin-prick test or a blood test for allergen-specific IgE can show sensitisation: evidence that the immune system recognises an allergen. Clinical allergy requires a compatible pattern of symptoms linked to a plausible exposure.
A positive skin-prick response or detectable allergen-specific IgE indicates sensitisation to the tested allergen, according to that test’s method and interpretation criteria.
Symptoms occur in a reproducible and biologically plausible relationship to exposure. The history links the test result to the patient’s real-life symptoms.
Do not label a patient allergic, prescribe avoidance or recommend a major treatment change from an isolated positive test. Interpret the result with the history and examination.
When should testing be considered?
Start with the clinical question. A focused history and examination may be enough to begin appropriate symptom management. Testing is more useful when the diagnosis is uncertain, symptoms persist or recur, an allergen-directed plan may help, or confirmation is needed before considering specialist treatment such as allergen immunotherapy. Select only allergens that are plausible from the exposure history and are available through the local laboratory or testing service.
- Features that may support allergic rhinitis: recurrent sneezing, nasal or eye itching, watery rhinorrhoea, congestion and a pattern linked to a season, environment, animal, occupation or other reproducible exposure.
- Features that need a wider differential: isolated obstruction, unilateral symptoms, persistent thick or purulent discharge, facial pain, recurrent bleeding, loss of smell, medication-related symptoms or a visible structural abnormality.
- A useful reason to test: the result is expected to help distinguish allergic from non-allergic disease, guide a realistic avoidance discussion, or support a specialist treatment decision.
- A weak reason to test: screening a person with no compatible symptoms, ordering a large panel “just to check,” or testing an allergen that has no plausible relationship to the patient’s exposure.
Take a focused allergy history first
Ask what happens, when it happens and what the patient was exposed to. A precise history improves the choice and interpretation of the test. Do not assume that every blocked or runny nose is allergic: infections, irritants, non-allergic rhinitis, medication effects and structural causes can produce overlapping symptoms.
| History area | Questions to ask | Why it helps |
|---|---|---|
| Symptoms | Is there sneezing, itching, watery discharge, congestion, eye symptoms, cough or wheeze? | Helps establish whether an IgE-mediated pattern is plausible and whether other airway disease needs assessment. |
| Timing and pattern | When did symptoms begin? Are they seasonal, persistent, intermittent, nocturnal or linked to a particular task or place? | Connects symptoms to possible exposure and distinguishes a consistent pattern from a coincidental test result. |
| Exposure | What changes at home, school, work or outdoors? Are symptoms reproducible around animals, dust, mould, smoke, sprays or other exposures? | Guides a short, relevant test selection. Use allergens and extracts available and appropriate to the local service. |
| Impact and associated disease | How are sleep, study, work and daily activities affected? Is there asthma, eczema, previous severe reaction or treatment failure? | Shows the clinical importance and whether a more experienced or multidisciplinary review is needed. |
| Medicines and previous tests | Which prescribed and over-the-counter medicines are used? Were prior allergy tests done, and under what conditions? | Some medicines can suppress skin-test responses; previous results should be checked for method and clinical relevance. |
Main tests used in suspected allergic rhinitis
| Test | What it measures | Common role | Main limitation |
|---|---|---|---|
| Skin-prick test (SPT) | A local skin response after a small amount of selected allergen is introduced at the skin surface. | Demonstrates sensitisation to selected allergens; results are usually available during the visit. | Requires suitable skin, trained staff, valid controls and a protocol. Medicines and skin conditions can affect interpretation. |
| Serum allergen-specific IgE | IgE in a blood sample that binds to a selected allergen or allergen component, as reported by the assay. | Useful when skin testing is not suitable, cannot be interpreted reliably, or is not available. | Results depend on the assay and selected allergens. Detectable IgE is sensitisation, not automatic proof of symptomatic allergy. |
| Total serum IgE | The overall amount of IgE measured in serum, not the amount directed at one specific allergen. | May help interpret selected situations when requested by a clinician. | It does not identify the causative allergen and is not a stand-alone test for allergic rhinitis. |
| Specialist nasal allergen challenge | A supervised nasal response to a selected allergen, assessed using a specialist protocol. | Reserved for selected specialist questions when history and routine tests do not resolve the diagnosis. | Not a routine clinic screening test; it needs trained supervision, defined indications and appropriate monitoring. |
Skin-prick testing: principles and supervised workflow
Skin-prick testing is a controlled procedure, not a home test. A trained provider applies selected allergen extracts and controls to suitable skin, introduces each test according to the service protocol, and reads the responses at the specified time. Exact extracts, spacing, device, timing and measurement criteria differ between services; follow the locally approved method rather than mixing protocols.
- Confirm the reason and consent. Review the history, explain that the test detects sensitisation, discuss expected local itching or swelling and the rare possibility of a more serious reaction, and obtain consent.
- Check suitability. Review medicines, skin condition, past reactions and the patient’s current clinical stability. Ask the testing service which medicines may affect its protocol. If testing is unsuitable or the result may be unreliable, discuss another pathway with a qualified clinician.
- Choose relevant allergens. Use a focused selection based on symptoms and plausible exposures. Use in-date, correctly stored reagents and the test service’s validated device and procedure.
- Use controls and prevent mix-ups. Include the protocol’s positive and negative controls. Label each site clearly, keep applicators separate and avoid transferring extract between sites. If controls fail or the sites cannot be identified, do not interpret the panel as valid.
- Read and document as directed. At the specified interval, assess the local response using the service’s criteria. Record the allergen, control responses, result, method, relevant medicines and any symptoms or limitations.
- Observe and provide advice. Follow the service’s observation and aftercare procedure. Explain that a positive response needs correlation with symptoms and that a negative result does not exclude every possible allergic mechanism.
Controls matter: The positive control checks whether the skin can produce a response under the test conditions; the negative control helps identify background reactivity. If the positive control is suppressed or the negative control is reactive, the results may be difficult to interpret. The testing clinician should document the limitation and decide whether another test is appropriate.
Factors that affect a skin-test result
Antihistamines and some other medicines may reduce skin responses. The effect and required interval depend on the drug and the testing protocol. Patients should not stop a prescribed medicine on their own; the clinician or testing service should give instructions.
Extensive eczema, dermographism, irritation, scarring or other skin changes can make results difficult to read. A clinician should decide whether another site or serum testing is more appropriate.
Expired, poorly stored or unsuitable extracts, inconsistent technique, site mix-ups and incorrect timing can create misleading results. Follow the manufacturer and local laboratory or allergy-service requirements.
Serum allergen-specific IgE testing
A laboratory measures IgE that binds to selected allergens. The request should name plausible allergens and include relevant clinical information according to the receiving laboratory’s requirements. Serum-specific IgE testing is often considered when skin tests cannot be performed or read reliably, when a relevant medicine cannot safely be interrupted for skin testing, or when skin testing is unavailable. Antihistamine treatment does not generally alter the serum-specific IgE result, but all medicines and relevant clinical details should still be recorded.
Read the report using the laboratory’s assay, units and reference information. Do not use a single universal cut-off for every allergen, laboratory or clinical question. A low positive may be irrelevant; a stronger result can make clinically relevant sensitisation more likely in the right context, but the numerical level does not predict how severe a future reaction will be. A negative result reduces support for sensitisation to the allergens tested, but it does not replace clinical review if the history remains concerning.
How to interpret results in context
| Finding | Possible meaning | Clinical approach |
|---|---|---|
| Positive test and matching exposure-linked symptoms | Relevant IgE sensitisation may help explain the clinical pattern. | Discuss how well the timing, setting and symptoms match. Use the result as one part of a management plan. |
| Positive test but no symptoms with exposure | Asymptomatic sensitisation, cross-reactivity or a clinically irrelevant positive result. | Do not label a clinical allergy or recommend broad avoidance from the test alone. |
| Negative test but a convincing history | The tested allergens may not include the trigger; the test may be affected by method or timing; another diagnosis or specialist phenotype may be present. | Recheck the history, selection and test validity. Seek senior, allergy or ENT advice if the result would change care. |
| Positive and negative controls are invalid | The skin-test panel may not be interpretable. | Document the limitation and arrange a suitable repeat or alternative only through the testing service. |
| Several weak positives from a large panel | Incidental sensitisation, cross-reactivity or findings of uncertain relevance are possible. | Return to the history; avoid treating a list of test results as a list of confirmed allergies. |
Interpretation example: A student has itchy eyes and sneezing mainly while cleaning a particular storeroom. A positive test to one aeroallergen is useful only if that allergen is plausible in the setting and the timing fits. If the same student has a positive result to an unrelated allergen but tolerates ordinary exposure without symptoms, that finding alone does not establish clinical allergy.
Tests and practices that should not be used as routine allergy screening
- Untargeted panels: broad testing without a compatible history can identify irrelevant sensitisation, create anxiety and lead to unnecessary restrictions or referrals.
- Total IgE by itself: does not identify which allergen is relevant and cannot confirm allergic rhinitis alone.
- Food panels for isolated rhinitis: food-specific IgE should not be requested to explain nasal symptoms without a compatible food-reaction history. Food test positivity can lead to avoidable dietary restriction.
- IgG “food sensitivity” tests and non-validated methods: these do not establish IgE-mediated allergy and may prompt inappropriate diagnosis or treatment.
- Intradermal testing for routine aeroallergen screening: this is more sensitive in selected settings but may produce results of uncertain significance; its use belongs to a trained specialist pathway, not general screening.
- Unsupervised allergen challenge: inhaled, nasal, food or medication challenges can provoke a significant reaction and should only occur for a defined indication under appropriately trained specialist supervision.
Common errors and safer practice
| Error | Why it matters | Safer practice |
|---|---|---|
| Ordering a test before taking a history | The panel may not include a relevant allergen or may find unrelated sensitisation. | Document symptom pattern, timing and plausible exposure first; request only tests that answer the clinical question. |
| Calling every positive result an allergy | Sensitisation can occur without symptoms when exposed. | Check real-world exposure, symptom timing and reproducibility before assigning a clinical diagnosis. |
| Advising a patient to stop medicines without checking | Interruption can worsen the patient’s condition, and the necessary interval varies. | Ask the testing service to provide medicine-specific instructions and discuss safety with the prescribing clinician. |
| Ignoring invalid controls or an unsuitable skin site | A suppressed or reactive control can make test results unreliable. | Record controls and site suitability; let the trained tester determine whether results can be interpreted. |
| Using an IgE value to predict reaction severity | The concentration does not reliably grade the severity of an individual’s future reaction. | Use history and specialist assessment for risk; do not reassure or alarm on a number alone. |
Clinical examples
A patient reports repeated sneezing, nasal itching and watery eyes during a recurring outdoor season. Take a focused exposure history and examine for other causes. If confirming a relevant aeroallergen would change counselling or specialist treatment, a clinician may select skin-prick testing or serum-specific IgE.
A test panel detects sensitisation to an allergen, but the patient reports no symptoms during normal exposure. Record the result accurately, explain the difference between sensitisation and allergy, and avoid unnecessary avoidance advice.
A patient is taking a medicine that may suppress a skin response and cannot safely stop it without advice. Do not assume a negative skin panel is valid. Ask the testing service or supervising clinician whether serum-specific IgE or another assessment is more suitable.
Documentation checklist
- Record the symptom pattern, onset, timing, exposure and relevant associated conditions.
- State the clinical question and why testing is likely to change care.
- List the allergens requested and the basis for choosing them.
- For skin tests, document method, site, extracts, controls, timing, measurements or service interpretation, medicines and limitations.
- For serum tests, record the laboratory, allergen, assay result, units and relevant clinical information.
- Document interpretation in context, advice given, follow-up, referral or the plan to discuss uncertain results with a senior clinician or laboratory.
Clinical sequence: Focused history → decide whether the test will answer a useful question → select only relevant allergens → use a validated test through the appropriate service → check controls and limitations → interpret sensitisation alongside exposure-linked symptoms → document the plan.
Quick self-test
- What is the difference between sensitisation and clinical allergy?
- What should guide the selection of allergens for a test panel?
- When might serum allergen-specific IgE be considered instead of skin-prick testing?
- Why are positive and negative controls important in a skin-prick test?
- Can the concentration of allergen-specific IgE predict how severe a future reaction will be?
- Why should broad, untargeted panels and food IgE tests be avoided for isolated rhinitis?
Suggested answers
- Sensitisation means the test detects allergen-specific IgE or a skin response; clinical allergy requires compatible symptoms linked to a plausible exposure.
- The symptom and exposure history, the clinical question and the allergens available through the local testing service.
- When skin testing is unsuitable, cannot be interpreted reliably, is unavailable, or interfering medicines cannot safely be changed under the testing protocol.
- They help establish whether the skin can respond and whether background reactivity is present; invalid controls can make results unreliable.
- No. A value may support the likelihood that sensitisation is relevant in context, but it does not predict reaction severity.
- They may detect irrelevant sensitisation and lead to unnecessary anxiety, referrals or restrictions; test selection should follow a compatible history.
Key points
- Take a focused allergy history before ordering allergen tests.
- Skin-prick testing and serum-specific IgE detect sensitisation; neither proves clinical allergy by itself.
- Use skin tests through trained services with valid controls, appropriate reagents and local safety procedures.
- Serum-specific IgE is a useful alternative when skin testing is unsuitable or unreliable; interpret it using the assay and clinical history.
- Do not use total IgE, broad panels, food tests for isolated rhinitis or non-validated tests as general screening.
- Test values do not predict the severity of a future allergic reaction.
References and further reading
- American Academy of Allergy, Asthma & Immunology (AAAAI). Allergy Testing. Patient guidance on test types, history, skin testing and serum tests.
- Scadding GK, et al. BSACI guideline for the diagnosis and management of allergic and non-allergic rhinitis. Clinical & Experimental Allergy. 2017.
- Health Service Executive, Ireland. Indications for the Measurement of Allergen Specific IgE in General Practice and Non-Specialist Settings. Advice note, 2024.
- Dykewicz MS, et al. Rhinitis 2020: A practice parameter update. Journal of Allergy and Clinical Immunology. 2020.
Class notes: Coming soon.
Educational note: This page is for medical education and revision. It does not replace supervised clinical skills training, a qualified clinician’s assessment, current local laboratory instructions or emergency care.
