Presentation: Allergies

Question 1

What is the skin prick test?

Answer 1

The most commonly used allergy test that is easy to perform and inexpensive. Drops of diluted allergen are placed on the skin, and the skin is pierced with a needle. A wheal will typically develop if a patient has an allergy. Results can be interpreted after 15 minutes.

Useful for food allergies and pollen.

Question 2

What controls are included in the skin prick test?

Answer 2

The test normally includes a histamine (positive) and sterile water (negative) control.

Question 3

What is the radioallergosorbent test (RAST)?

Answer 3

A test that determines the amount of IgE that reacts specifically with suspected or known allergens, with results graded from 0 (negative) to 6 (strongly positive).

Useful for food allergies, inhaled allergens (e.g. pollen), and wasp/bee venom.

Question 4

When are blood tests used for allergy testing?

Answer 4

Blood tests may be used when skin prick tests are not suitable, for example, if there is extensive eczema or if the patient is taking antihistamines.

Question 5

What is skin patch testing?

Answer 5

A test useful for contact dermatitis where around 30-40 allergens are placed on the back. The patches are removed 48 hours later, and results are read by a dermatologist after a further 48 hours.

Question 6

What additional substances may be tested in skin patch testing?

Answer 6

Irritants may also be tested for during skin patch testing.

Question 7

What is Oral Allergy Syndrome (OAS)?

Answer 7

OAS, also known as pollen-food allergy, is an IgE-mediated hypersensitivity reaction to specific raw, plant-based foods including fruits, vegetables, nuts, and certain spices.

Question 8

What are the typical symptoms of OAS?

Answer 8

Symptoms typically include mild tingling or pruritus of the lips, tongue, and mouth.

Question 9

What initiates the hypersensitivity reaction in OAS?

Answer 9

The hypersensitivity reaction is initiated by cross-reaction with a non-food allergen, most commonly birch pollen.

Question 10

Why does cooking food prevent OAS symptoms?

Answer 10

Cooking denatures the proteins in the food, preventing the symptoms from occurring.

Question 11

How does OAS differ from food allergies?

Answer 11

OAS is caused by cross-sensitisation to a structurally similar allergen present in pollen, while food allergies are caused by direct sensitivity to a protein in food.

Question 12

What types of foods do not cause OAS?

Answer 12

Non-plant foods do not cause OAS because there are no cross-reactive allergens in pollen that are structurally similar to meat.

Question 13

What are the systemic symptoms more likely associated with food allergies?

Answer 13

Food allergies are more likely to cause systemic symptoms such as vomiting and diarrhoea and may lead to anaphylaxis.

Question 14

What is the prevalence of OAS in the UK?

Answer 14

About 2% of the UK population has OAS, but it is likely under-diagnosed.

Question 15

What associations are commonly linked with OAS?

Answer 15

Common associations include birch pollen allergy, rye grass pollen allergy, and rubber latex allergy.

Question 16

What should be suspected in patients with seasonal allergy symptoms who develop symptoms after eating raw food?

Answer 16

OAS should be suspected in these patients.

Question 17

What are the most common symptoms of OAS?

Answer 17

The most common symptoms are itching and tingling of the lips, tongue, and mouth.

Question 18

What happens to symptoms of OAS after contact with the allergen?

Answer 18

Symptoms fully resolve within one hour of contact.

Question 19

What are the visible signs during OAS episodes?

Answer 19

Most patients will have no visible signs, but some may have swelling and redness of the lips, tongue, and oral mucosa.

Question 20

How is OAS diagnosed?

Answer 20

OAS is a clinical diagnosis, but tests like IgE RAST and skin prick testing can be used to rule out other diagnoses.

Question 21

What is the management for OAS?

Answer 21

Avoidance of culprit foods is the primary management; oral antihistamines can be taken if symptoms develop.

Question 22

What should be done if symptoms of anaphylaxis develop?

Answer 22

An ambulance should be called, and intramuscular adrenaline may be required.

Question 23

What should patients be informed about cooked foods?

Answer 23

Patients should be informed that once cooked, culprit foods should not cause symptoms.

Question 24

What are the two broad categories of allergic reactions to venom?

Answer 24

Allergic reactions to venom may be broadly considered as either local or systemic.

Question 25

What defines a local allergic reaction to venom?

Answer 25

Redness, swelling, and pain limited to the skin and soft tissues directly related to the site of venom exposure, but spreading >10 cm from the site.

Question 26

What are examples of systemic reactions to venom?

Answer 26

Systemic reactions may refer to widespread redness, itching, urticaria, and/or angioedema (not affecting the mouth or throat).

Question 27

How should anaphylaxis be managed?

Answer 27

Anaphylaxis should be managed with intramuscular adrenaline, intravenous steroids, and intravenous anti-histamines as required. Oxygen and nebulised bronchodilators may also be required.

Question 28

Who should be referred to an allergy specialist?

Answer 28

People who’ve had a systemic reaction to an insect bite should be referred to an allergy specialist.

Question 29

When is testing for venom allergy recommended?

Answer 29

Testing for venom allergy is recommended in any patient with a history of a systemic reaction causing airway compromise or haemodynamic instability.

Question 30

What should patients with a history of a systemic reaction be provided with?

Answer 30

Patients with a history of a systemic reaction should be provided with a self-management plan, including guidance on the use of anti-histamines and adrenaline auto-injectors.

Question 31

What is venom immunotherapy (VIT)?

Answer 31

Venom immunotherapy (VIT) is considered to be one of the most effective immunotherapies in use for patients with a history of a previous reaction presenting with airway and/or haemodynamic compromise.

Question 32

What does the British Society for Allergy and Clinical Immunology advise regarding VIT?

Answer 32

VIT should not be performed in patients without demonstrable venom-specific IgE or in those with a recent history of anaphylaxis or systemic reaction.

Question 33

What should be performed to exclude indolent mastocytosis?

Answer 33

A baseline tryptase level should also be performed to exclude indolent mastocytosis.

Question 34

What is the success rate of VIT in preventing systemic reactions?

Answer 34

‘VIT is 95-100% and about 80% successful in preventing systemic reactions in wasp and bee sting allergy respectively.’