immunology

Question 1

Skin prick test:
-how is this done?
-what does this include?
-what is this useful for?

Answer 1

Most commonly used test as easy to perform and inexpensive. Drops of diluted allergen are placed on the skin after which the skin is pierced using a needle. A large number of allergens can be tested in one session. Normally includes a histamine (positive) and sterile water (negative) control. A wheal will typically develop if a patient has an allergy. Can be interpreted after 15 minutes

Useful for food allergies and also pollen

Question 2

RAST testing
-what is this?
-how are results given?
-What is this useful for?
-When may this be used>?

Answer 2

Determines the amount of IgE that reacts specifically with suspected or known allergens, for example IgE to egg protein. Results are given in grades from 0 (negative) to 6 (strongly positive)

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

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 3

What is skin patch testing? what is this useful for?

Answer 3

Useful for contact dermatitis. Around 30-40 allergens are placed on the back. Irritants may also be tested for. The patches are removed 48 hours later with the results being read by a dermatologist after a further 48 hours

Question 4

Doses of adrenaline:
-<6mths
-6mth to 6yrs
-6-12 year
->12yrs

Answer 4

< 6 months 100 - 150 micrograms (0.1 - 0.15 ml 1 in 1,000)
6 months - 6 years 150 micrograms (0.15 ml 1 in 1,000)
6-12 years 300 micrograms (0.3ml 1 in 1,000)
Adult and child > 12 years 500 micrograms (0.5ml 1 in 1,000)

Question 5

What 3 things should happen post-anaphalaxis

Answer 5

all patients with a new diagnosis of anaphylaxis should be referred to a specialist allergy clinic
an adrenaline injector should be givens an interim measure before the specialist allergy assessment (unless the reaction was drug-induced)
patients should be prescribed 2 adrenaline auto-injectors
training should be provided on how to use it
a risk-stratified approach to discharge should be taken as biphasic reactions can occur in up to 20% of patients

Question 6

Who can get a fast-track discharge after anaphalaxis 2 hrs?

Answer 6

fast-track discharge (after 2 hours of symptom resolution):

good response to a single dose of adrenaline
complete resolution of symptoms
has been given an adrenaline auto-injector and trained how to use it
adequate supervision following discharge

Question 7

who can get a fast-tracked discharge after anaphalaxis 6 hrs?

Answer 7

minimum 6 hours after symptom resolution

2 doses of IM adrenaline needed, or
previous biphasic reaction

Question 8

Who can get a fast-tracked discharge after anaphalaxis 12hrs?

Answer 8

minimum 12 hours after symptom resolution

severe reaction requiring > 2 doses of IM adrenaline
patient has severe asthma
possibility of an ongoing reaction (e.g. slow-release medication)
patient presents late at night
patient in areas where access to emergency access care may be difficult
observation for at 12 hours following symptom resolution

Question 9

What is oral allergy syndrome strongly linked with? does it present at certain times of year?

Answer 9

This explains why OAS is strongly linked with pollen allergies and presents with seasonal variation.

Question 10

How does oral allergy syndrome differ from food allergy?

Answer 10

A food allergy is caused by direct sensitivity to a protein present in food. OAS is caused by cross-sensitisation to a structurally similar allergen present in pollen.

Question 11

How common is oral allergy syndrome?

Answer 11

About 2% of the UK population has OAS but this is probably under-diagnosed.
About 1/2 of patients with a general pollen allergy and 3/4 of patients with an allergy to birch pollen (the most common allergen in the UK) report symptoms of OAS

Question 12

What are three assoc. with oral allergy syndrome?

Answer 12

Associations:

Birch pollen allergy (most common)
Rye grass pollen allergy
Rubber latex allergy

Question 13

Presentations of oral allergy syndrome:
-what history to look out for?
-what are the symptoms?
-How long do symptoms last?
-what is a rare complication?

Answer 13

OAS should be suspected in patients with a history of seasonal allergy symptoms (rhinitis, conjunctivitis and asthma) who present with symptoms minutes after eating a specific raw food.
Itching and tingling of the lips, tongue and mouth are the most common symptoms
Mild swelling and redness of the lips, tongue and throat may occur.
In severe cases, patients develop nausea and vomiting.
Symptoms fully resolve within one hour of contact.
Anaphylaxis is a very rare complication.

Question 14

What are three signs of OAS?

Answer 14

Most patients will have no visible signs during or between episodes of OAS.
Some patients may have visible swelling and redness of the lips, tongue and oral mucosa.
Patients with anaphylaxis present with wheeze, hives, hypotension and collapse.

Question 15

What investigations are used for OAS?

Answer 15

OAS is a clinical diagnosis but further tests can be used to rule out diagnoses such as food allergies and to confirm the diagnosis when the history is unclear.
Standard IgE RAST and skin prick testing may be performed to identify common allergens such as pollens which co-exist with OAS. Note that common pollen allergies have specific associated foods which cause OAS. For example, birch allergy is associated with sensitivity to, amongst others, carrot, parsley and spinach.
Food-specific IgE testing: this is unreliable and rarely performed clinically because the food does not survive processing.
Skin prick testing with culprit foods is more commonly used. A positive test would cause a small, itchy lump to develop on the skin.

Question 16

What are 4 steps in management of OAS?

Answer 16

Avoidance of culprit foods is the only required modification for the vast majority of patients.
If culprit food is eaten and symptoms develop, an oral antihistamine can be taken.
If symptoms of anaphylaxis develop, an ambulance should be called. Intramuscular adrenaline may be required.
Patients should be informed that once cooked, culprit foods should not cause symptoms.

Question 17

When does venom allergy warrant referral?

Answer 17

Referral to an allergy specialist should be made (with urgency depending on clinical judgement) for people who have had, or are suspected of having, a systemic reaction to an insect bite or sting.

Question 18

Who gets testing for venom allergies? what should patients be advised?

Answer 18

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

It may also be beneficial in patients with a history of a systemic cutaneous reaction where the allergen is felt to be difficult to avoid e.g. an allergy to bee stings in a beekeeper.
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.
Patients should also be advised to wear a medical alert device.

Question 19

What is the treatment for venom allergy? who gets this?

Answer 19

Venom immunotherapy (VIT) is considered to be one of the most effective immunotherapies in use and may be recommended for patients with a history of a previous reaction which presented with airway and/or haemodynamic compromise and raised levels of venom-specific immunoglobulin E on either skin prick or in vitro testing.