Allergy

Question 1

What must happen for an allergic reaction to occur ?

Answer 1

1) Immune activation to the allergen- sensitisation
2) Production of specific IgE to the allergen
3) Binding of sufficient specific IgE to mast cell high affinity IgE Fc receptor
4) Re-encountering the allergen that crosslinks the specific IgE bound to the IgE Fc receptors on Mast cells
5) Degranulation of those mast cells

Question 2

What are common differentials for a food allergy ?

Answer 2

Metabolic issues e.g. lactose intolerance
Pharmocological issues e.e. histamine containing/releasing foods, caffeine
Toxins e.g. infection
Others e.g. IBS, GI reflux, infectious urticaria

Can be hard to tell if alergy or not, can ask if antihistamine helps or time before onset

Question 3

What is anaphylaxis ?

Answer 3

Severe systemic allergic reaction.

Involves one or both of two severe features:
-Respiratory difficulty (which may be due to laryngeal oedema or asthma)
-Hypotension (which can present as fainting, collapse, or loss of consciousness).

Other features are usually present.
-Urticaria

Generally aeroallergens do not induce anaphylaxis

Question 4

How are allergies tested for in the lab ?

Answer 4

specific IgE (e.g. ISAC/MADAlex)
total IgE
Mast cell tryptase

Question 5

How are allergies tested for in a clinical setting ?

Answer 5

Skin prick testing

Question 6

What is skin prick testing ?

Answer 6

Stab some allergen into skin and then measure size of reaction and compare to a positive (histamine) and negative (saline) control
-Forearm used in adult and back used in baby

Question 7

Describe total IgE testing

Answer 7

Pretty useless bears no relation to levels of specific IgE
-Only really used to find baseline prior to anti IgE therapy for dosing calculation
-Can be elevated in vasculitis

Question 8

What is a potential diagnostic issue with raised specific IgE ?

Answer 8

Specific IgE levels for foods are frequently raised in patients with eczema and are commonly falsely positive or clinically irrelevant.
-Without a history suggestive of immediate allergy, positive results should be treated with caution
-Screening for food allergies by measuring specific IgE alone is therefore inappropriate

Question 9

Describe specific IgE testing

Answer 9

Immunoassay that measures allergen specific IgE
-Gives a quantitative result
->0.35KuA/L is regarded as elevated with a sliding scale of probable clinical significance depending on concentration.
-A grade 6 result means a higher level of sensisitsation than a grade 0
-Single allergens compared with mixes and components

Question 10

What are sensitivity and specificity in testing ?

Answer 10

Sensitivity = How good a test is at detecting true positives (%)
Specificity = How good a test is at identifying true negatives (%)

Question 11

What are examples of types of specific IgE testing ?

Answer 11

ISAC/MADAlex
-Microarray/chips
-Used to determine severe allergies which can cause angiodema or anaphylaxis
-Useful if is difficult to find cause
-Used to find specific allergin protein (molecular components) within foods

Question 12

What is mast cell tryptase ?

Answer 12

Mast celll tryptase is released during allergic reactions
-Is diagnostic for anaphylaxis
-Useful in food and venom allergies, not as good in foods
-Elevated baseline increases risk of severe allergic reaction

Is also elevated in renal disease

He starts in anaphylaxis, its gets worse, it gets better

Question 13

What is antigen challenge testing ?

Answer 13

Antigen challenge testing safely re-exposes a patient to a suspected allergen to confirm hypersensitivity when lab tests are uncertain — performed only under strict medical monitoring.
-Also used to confirm dianoses
-A successful food challenge means they can go back to eating it

Question 13

What are pollen food syndromes ?

Answer 13

Plant pollen allergies causing allergy to foods due to cross reactions
-initially alergy will be hayfever but then becomes food
-cross reactions here are immune system mistaking food antigens for polllen antigens

these allergies are generally more limited to oral cavity - anaphylaxis is rare

Question 14

What is alpha gal ?

Answer 14

Alpha gal allergy is reaction to mamillian meat
-Tick bites carry antigens from previous meat into us
-Alpha gal carb is attached to protein of some mammals, partifcuarly offal
-We make specific IgE to alpha gal; allergy to mammilian meat

Question 15

What is unique about an alpha gal allergy ?

Answer 15

Stomach takes 2-4 hours to digest and absorb meat and then cause the reaction
-Only type of actually delayed allergy
-Can get anaphylaxis in bed

Question 16

What events are suggestive of an alpha gal allergy ?

Answer 16

BBQs
-Eat a lot of meat
-Drink alcohol which is a cofactopor

Question 17

What do cofactors do in an allergy ?

Answer 17

Can increase the severity of an allergic reaction

Question 18

How can allergies be treated ?

Answer 18

Desentisisation/immunotherapy

Question 19

How does desentisisation work ?

Answer 19

By retraining the immune system:
-Repeated low-dose allergen exposure shifts the response from Th2/IgE-mediated allergy to a tolerant, Treg/IgG4-dominant state, so mast cells and basophils become less reactive and allergic symptoms diminish.