IOD Allergy

Question 1

What is an allergy?

Answer 1

An IgE mediated Type I hypersensitivity reaction.

Question 2

What is atopy?

Answer 2

Genetic tendency to produce specific IgE antibodies on exposure to common
environmental antigens (house dust mite, cat, grass pollen, foods etc.)
1 in 4 people in the UK have this

Question 3

clinical allergy?

Answer 3

Commonly affects the nose, eyes (hayfever), chest (allergic asthma), skin (hives,
wheals, angioedema and exacerbation of atopic eczema).

Question 4

Food allergies?

Answer 4

Food allergies may produce a spectrum of allergic symptoms ranging from mild
symptoms (oral itching, tingling and hives) to bronchospasm, wheezing, laryngeal
oedema and life threatening circulatory collapse (see under ‘anaphylaxis’).

Question 5

Type 1 hypersensitivity

Answer 5

Specific IgE attaches to the Fc(epsilon) receptors on Mast cells. Cross linkage of bound
Specific IgE by allergen leads to degranulation of the mast cell and rapid release of preformed-mediators (e.g histamine).
On activation, the mast cell ‘degranulates’ and releases inflammatory mediators.
‘Pre-formed mediators’ which include histamine, tryptase and heparin, are released
rapidly.
‘Synthesised mediators’ which include leukotrienes and prostaglandins, are released
slowly.
Mast cells can also be activated directly (without Specific IgE involvement)
e.g by direct binding of radiocontrast dye, opiates etc. to the mast cell.
mast cells are found everywhere in the body-widespread reactions

Question 6

Effects of histamine release?

Answer 6

Pruritis –histamine is highly pruritogenic
Vasodilation and leakage of fluid- hives, angioedema, drop in BP
Smooth muscle contraction- bronchospasm,wheezing
Histamine exerts these effects through histamine receptors.
Widespread, rapid systemic release of mediators (particularly histamine) will cause
capillary leakage and mucosal oedema, and may result in circulatory collapse as well as
respiratory compromise due to bronchospasm.

Question 7

Diagnosis?

Answer 7

Detailed clinical history is crucial in planning allergy tests.
e.g. Time course of allergic reaction, suspected triggers, seasonality of symptoms, location where symptoms are worse (indoors, outdoors, town, countryside etc).
• Detection/Measurement of Specific IgE is done by one of 2 methods:-
NB: Suspect allergens for testing are selected on the basis of clinical history.
1. Skin Prick testing (SPT): In-vivo test. Not advised in patients with extensive
eczema, patients who cannot stop antihistamine treatment or any other immune
modulatory treatment. Results are expressed as ‘positive’ or ‘negative’ to
individual allergens
Measurement of allergen-Specific IgE in serum sample (previously
known as IgE ‘RAST’): Results are expressed in kUA/L. (In adults, > 0.35
kUA/L is regarded as a positive result).
NB: Results of SPT and Blood tests are largely concordant.
Positive results by either test only confirms ‘IgE sensitisation’. This may/may not be associated with ‘clinical allergy’.

Component Specific IgE: Newer developments include measurement of Specific IgE to some of the many protein components of individual allergens:
e.g. peanut storage proteins Ara h1, Ara h2, Ara h3, and pollen cross- reactive peanut protein Ara h8, to help distinguish between true allergy and ‘oral allergy syndrome’ to peanut.

Question 8

Blood test?

Answer 8

In vitro laboratory test: sample of blood is analysed in the laboratory
Several allergens can be tested on a single blood sample
Results in hours or days
Not affected by anti-histamine medications
Numerical result (KuA/l)
Skin condition does not affect the test.
More expensive
Suitable for any age

Question 9

skin prick test

Answer 9

In vivo test: done on the patient’s skin by trained staff (in clinic)
Multiple skin pricks (one for each allergen)
Result in 15-20 minutes
Anti-histamine must be stopped for 5-7 days before SPT
Measurement of wheal (mm)
Avoid in skin disease (e.g. extensive eczema)
Could be less expensive
Technical difficulties in very young.

Question 10

Serum total IgE?

Answer 10

Serum Total IgE
Levels above the age-related reference range simply indicate an atopic disposition, and
does not require further investigation.
NB: A ‘normal’ Total IgE may be associated with a positive Specific IgE result to one or
more allergens.
Therefore, Total IgE must not be used as a ‘screening test’ for allergy.

Question 11

Serum Tryptase?

Answer 11

Serum Tryptase
Useful ‘marker’ of mast cell degranulation. High levels are seen soon after an anaphylactic reaction.
Tryptase has a short half-life in vivo. Ideally, a blood sample should be taken at between 15min and 3 hours after the onset of the reaction. A second sample can be taken at 3- 6h after the reaction when increased levels are still usually detected.
Tryptase levels return to baseline around 12-14 hours. A third sample between 24-48 hours can be tested to check base-line levels.
Persistently elevated baseline level of tryptase is a feature of Mastocytosis (rare)

Question 12

Challenge testing?

Answer 12

‘Double blind placebo control challenge’ with the suspect allergen (usually a food
allergen) is regarded as the ‘gold standard’ for diagnosis.
It is labour intensive, time consuming and could be stressful for the patient, and is therefore done only in specific situations (e.g. doubt about the diagnosis when the clinical history of a reaction is associated with negative Specific IgE results)

Question 13

What does a positive specific IgE indicate?

Answer 13

IgE sensitisation to the allergen

Question 14

Do the IgE serums always exclude allergy?

Answer 14

no

Question 15

what does an elevated total IgE show?

Answer 15

atopy-only search for specific causes if noted in clinical history

Question 16

can you have a clinical allergy with normal total IgE?

Answer 16

yes

Question 17

Basophils?

Answer 17

Basophils are similar to mast cells (histamine granules, high- affinity IgE receptors etc) and when stimulated release mediators and express surface markers eg histamine, lipids and cytokines

Question 18

Basophil activation test?

Answer 18

BAT is an in vitro assay in which the activation of a patient’s basophils (e.g. expression
of CD63,CD203C) upon exposure to an allergen is measured by flow cytometry.
Used as an in vitro alternative to the time consuming ‘DBPC challenge test’ to foods,
drugs, venom etc
However, due to issues with standardisation and interpretation of results, the test is not
currently widely available in mainstream practice.

Question 19

ISAC?

Answer 19

ImmunoCAP ISAC is a multiplex in vitro diagnostic tool.
Biochip technology enables measurement of IgE antibodies to a fixed panel of 112
components from 51 allergen sources in a single step
Not currently recommended by NICE.

Question 20

Which tests should not be used in food allergy?

Answer 20

vega test
• applied kinesiology
• hair analysis.
serum-specific IgG

Question 21

Vega test?

Answer 21

involves measuring electro-magnetic conductivity in the body, using a galvanometer.
The patient has one electrode placed over an acupuncture point and the other electrode is held while a range of allergens and chemicals are placed in a metallic honeycomb.
A fall in the electromagnetic conductivity or a “disordered reading” is said to indicate an allergy or intolerance to that allergen

Question 22

Applied Kinesiology?

Answer 22

:The patient’s muscle strength (usually the deltoid) is tested for weakness when the allergen is placed in a vial in front of the patient.
If the patient is
unable to resist the counter pressure applied, the test is considered positive to that allergen.

Question 23

Hair analysis?

Answer 23

A sample of hair is tested for toxic levels of heavy metals and for
deficiencies of selenium, zinc etc. In another hair test called ‘dowsing’, a pendulum is
swung over the hair and an allergy is diagnosed if an altered swing is noted.

Question 24

IgG Allergy test ?

Answer 24

This test measures IgG and IgG4 antibodies to various foods.
However, the production of IgG antibodies to foods is a non-specific response, indicating exposure.
There is no convincing evidence to suggest that this test helps to diagnose allergy

Question 25

True food allergy?

Answer 25

IgE mediated de-granulation of mast cells.

Common food allergens: cow’s milk protein, egg, peanuts, tree nuts, fish, prawns

Question 26

‘Oral allergy syndrome’?

Answer 26

Due to cross reacting ‘pan-allergens’ which are found in various members of the plant family (fruits, vegetables, nuts etc). They are heat labile and destroyed by digestion, hence symptoms are usually limited to the oral cavity.

Question 27

“False food allergy”?

Answer 27

Direct stimulation of mast cells or histamine ingestion
Scromboid fish poisoning (scrombotoxicosis) – Histamine is released by bacterial action
(spoilage) on scromboid fish (e.g tuna).
Symptoms that mimic an allergic reaction occur when the spoiled fish containing histamine is consumed.

Question 28

“Food intolerance”?

Answer 28

adverse reaction to food, with no histamine related symptoms

e. g Lactose intolerance, gluten sensitivity
- umbrella term for all of the above

Question 29

“Food sensitivity”?

Answer 29

e. g Lactose intolerance, gluten sensitivity

- umbrella term for all of the above

Question 30

“Food aversion”-

Answer 30

psychological

Question 31

Diagnosis and management for food allergy?

Answer 31

Detailed clinical history
If there is clinical suspicion of an IgE mediated allergy,
perform investigations based on the clinical history
1) Specific IgE by blood tests or skin prick tests
2) Rarely, consider supervised oral food challenge
Diagnosis
Management
1) Avoid the food allergen
2) Carry emergency treatment

Question 32

misconception of eczema?

Answer 32

eczema/atopic dermatitis is ‘caused by a food
allergy’ and that extensive food allergy testing (Specific IgE detection by blood or skin
prick testing) may ‘reveal’ the food that must be avoided to cure the eczema.

Question 33

eczema pathophysiology?

Answer 33

It is now recognized that eczema is a chronic skin condition associated with filaggrin
gene mutations causing poor barrier function of the skin, which in turn allows IgE
sensitisation to aero-allergens and food allergens via a thinner, permeable epidermis.

Question 34

eczema and food allergy?

Answer 34

If there is a true food allergy (e.g. egg allergy, causing immediate peri-oral symptoms on contact with egg), it is not uncommon for eczema to flare up several hours after the allergic reaction

Question 35

Why should allergy testing in eczema be based on clinical history?

Answer 35

Blind testing for panels
of food allergens is NOT recommended. NB: ‘False’ positive specific IgE results are
common in individuals with eczema (and asthma), simply reflecting exposure and IgE
sensitisation in an atopic individual (and does not necessarily predict clinical allergy).

Question 36

irritants?

Answer 36

Soaps, detergents
➢Disinfectants (Chlorine)
➢Contact with
– Juices from fresh fruits, meats,
vegetables
– Chemicals, fumes on the job

Question 37

microbes?

Answer 37

Certain bacteria
– Staphylococcus aureus
➢Viruses
➢Certain fungi

Question 38

ALLERGENS?

Answer 38

➢House dust mites
➢Pets (cats, dogs)
➢Pollens (seasonal)
➢Moulds
➢Dandruff

Question 39

OTHERS?

Answer 39

➢Hot or cold temperatures
– Heat
– Humidity
– Perspiration from exercising
➢Foods
➢Stress
➢Hormones