What is Nasal Allergen Challenge?

Nasal Allergen Challenge (NAC) is a test using allergens sprayed directly into the patient’s nasal cavity in an appropriate amount to stimulate symptoms and assess the nasal mucosa’s response to the substance.

This test “simulates real-life conditions” that patients may encounter, such as inhaling house dust mites, flower pollen, mold, or animal dander, causing immediate allergic reactions. This method is therefore a key standard for directly confirming the diagnosis of allergic rhinitis.

Why should nasal challenge testing be done?

To confirm the diagnosis of allergic rhinitis when skin prick test or IgE specific blood test results are still unclear.
To diagnose Local Allergic Rhinitis, which occurs when patients have allergic rhinitis symptoms but skin or blood tests do not detect allergens.
To confirm that the patient has nasal allergic symptoms caused by that specific allergen, helping to plan treatment such as deciding whether the patient is suitable for Allergen Immunotherapy.
For research and evaluation of new drugs or treatment methods.

Preparation before the test: To obtain accurate results, patients should follow the doctor’s instructions, such as

Avoid using antihistamines for at least 7 days before the test.
Avoid using nasal steroid sprays as prescribed by the doctor.
Avoid using some decongestants or bronchodilators as they may suppress nasal response.
Avoid testing during respiratory infections such as colds or sinusitis.
Get enough rest and avoid heavy exercise before the test.

Advantages of Nasal Allergen Challenge (NAC)

Increases diagnostic accuracy by confirming results when other tests such as Skin prick test or IgE specific blood test are unclear, helping to identify whether symptoms are truly caused by allergies or other factors.
Assesses nasal mucosa sensitivity, indicating how quickly or severely the patient responds to allergens, helping to better classify the severity of allergic rhinitis.
Helps plan treatment by assisting decisions on whether the patient is suitable for Allergen Immunotherapy, allowing doctors to choose targeted and personalized treatment approaches.
Used in research and evaluation of new treatment methods.
Safe under medical standards, conducted by trained doctors and staff. The allergen dose is appropriately controlled to reduce the risk of severe reactions, and doctors can provide immediate assistance if abnormalities occur.

Who is suitable for the test?

Those suspected of having allergic rhinitis but with no detected allergens or unclear skin or blood test results.
Patients who suspect they are truly allergic to a specific allergen.
Those with multiple allergic symptoms who want to identify specific allergens.
Those preparing to receive Allergen Immunotherapy.
Asthma patients suspected that the allergen affects their asthma symptoms.
Patients involved in allergy and respiratory disease research.

Test procedure

1. Initial nasal assessment The doctor will use a nasal endoscope or light to check if the nasal mucosa is ready for testing, such as no nasal septum deformity.

2. Patient preparation Before the test, assess nasal function, measure vital signs, and evaluate symptom severity.

3. Allergen spray The amount used is strictly controlled according to standards.

4. Observation and measurement

Clinical symptoms such as nasal congestion, runny nose, sneezing, nasal or eye itching.

Assessment using Peak Nasal Inspiratory Flow device to measure nasal airway obstruction through nasal breathing.

5. If the test is positive, symptoms will be treated by the doctor, and the patient can go home the same day after symptoms improve.

Results

If the patient truly has allergic rhinitis, symptoms will appear clearly within 15–30 minutes after allergen exposure.
Identifies which allergen triggers symptoms, allowing doctors to give precise avoidance advice.
Confirms the relationship between symptoms and allergens detected by skin or blood tests.

Limitations of Nasal Allergen Challenge

This test is carefully supervised under the guidance of doctors and medical personnel.
Medications can be stopped before the test without affecting daily life.
The allergen dose is standardized to reduce risk.
Only one allergen can be tested at a time.
Possible symptoms include nasal allergy symptoms such as congestion, itching, runny nose, and sneezing.
In rare cases of severe symptoms such as difficulty breathing, the medical team is prepared to provide immediate care and medication.
Patients with chronic obstructive pulmonary disease, uncontrolled asthma, or pregnancy cannot undergo the test.

Managing allergic rhinitis is not just about relieving symptoms but finding the true cause for appropriate treatment. Nasal Allergen Challenge (NAC) is another method that helps doctors diagnose accurately and determine suitable treatment plans for you. At Phyathai 2 Hospital, you will be cared for by specialists in respiratory and allergy systems along with an experienced multidisciplinary team, using standardized diagnostic technology to help you understand your condition and plan comprehensive treatment, including diagnosis, treatment, and continuous follow-up.

Dr. Sasipa Saengkanjanavanich

Director of Allergy and Asthma Center

Phyathai 2 Hospital

Dr. Chalermchai Chumsaengchotisakul

Allergy and Clinical Immunology Specialist