Allergy

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Allergy
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• Role of mast cells
• Definition of allergy
• Hypersensivity reactions
• Diagnosis of allergy
• History
• Skin prick testing
• Blood IgE testing
• Mast cell tryptase
• Management of allergy

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Allergy is

• UK Allergy is immediate hypersensitivity
  mediated by IgE and mast cell degranulation (type
  I hypersensitivity).
• US Any hypersensitivity to exogenous substances
• Lay Any reaction to exogenous substances

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Allergy is

• Allergy is immediate hypersensitivity mediated by
  IgE and mast cell degranulation.

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Allergy is

• Allergy is immediate hypersensitivity mediated by
  IgE and mast cell degranulation.
• Mediators
• Enzymes MC tryptase
• Histamine (not respiratory MCs)
• Cytokines IL3, IL4
• Cyclo-oxygenase - prostaglandin
• Lipoxygenase pathway - leukotriene

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Allergy is not

• Mast cell degranulation from other causes
• Infection
• Opiates
• Nervous system
• NSAIDs

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Allergy is not

• Other forms of Hypersensivity
• Type II - Cyto toxic antibody - minutes

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Allergy is not

• Other forms of Hypersensivity
• Type II - Cyto toxic antibody
• Type III Immune complex - hours

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Allergy is not

• Other forms of Hypersensivity
• Type II - Cyto toxic antibody
• Type III Immune complex
• Delayed hypersensitivity- days

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Allergy Diagnosis

• History taking
• Timing
• Following exposure
• Seasonal
• Atopy history
• Personal
• Family
• Allergens
• Latex family, oral allergy syndrome, penicillins

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Allergy Diagnosis

• History taking
• Timing
• Following exposure
• Seasonal

Mackerel pate at wedding
5 seconds Nausea Aversion
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Allergy Diagnosis

• History taking
• Timing
• Following exposure
• Seasonal

Mackerel pate at wedding
5 seconds Nausea Aversion
5 minutes Lip swelling Allergy
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Allergy Diagnosis

• History taking
• Timing
• Following exposure
• Seasonal

Mackerel pate at wedding
5 seconds Nausea Aversion
5 minutes Lip swelling Allergy
4 hours DV Scrombo -toxin
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Allergy Diagnosis

• History taking
• Timing
• Following exposure
• Seasonal

Mackerel pate at wedding
18 hours DV Food poisoning
5 seconds Nausea Aversion
5 minutes Lip swelling Allergy
4 hours DV Scrombo -toxin
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Allergy Diagnosis

• History taking
• Timing
• Following exposure
• Seasonal

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Allergy Diagnosis

• History taking
• Atopy history
• Personal
• Family

Hay fever Asthma
Hay fever Nut allergy
Eczema Latex allergy
Insect venom and antibiotic allergy frequently
occur in non-atopic individuals
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Allergy Diagnosis

• History taking
• Allergens

Oral Allergy Syndrome Tree pollen Apple, pear,
peach
Grass pollen
Latex Kiwi Avocado Banana
Hazel Walnut Almond Brazil Peanut
Peas Beans
Bee Wasp
Penicillin Cephalosporin
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Skin prick testing
Histamine
Hazel
Milk
Soya
Peanut
Almond
Saline
Brazil
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Skin prick testing

• Advantages
• Cheap
• Quick
• Visible results for patients
• Can be used for allergens where in vitro testing
  not available
• Fresh fruits
• Drugs
• Egg
• Can be done in presence of steroids
  cromoglycate

• Disadvantages
• Requires trained staff resuscitation facilities
• Not possible in severe dermatographism or eczema
• Some drugs prevent reactions
• Antihistamines
• H2 blockade
• Tricyclics
• Benzodiazepines phenothiazines

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Total IgE

• Not particularly useful in isolation
• Not everyone with allergy has a raised total IgE
• Total IgE raised in non atopic situations
• Parasites
• Vasculitis
• Tumours

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Specific IgE testing

• Tests are tricky
• Specific IgE is present at 104-105 lower levels
  than other substances
• Most specific IgE may be bound to mast cells
• Allergen may be denatured eg fresh fruit

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SPT v IgE

• Confirmed by milk challenge Saarinen et al 2001

gt0.35u/l
3mm
gt0.7u/l
6mm
gt7.0u/l
8mm
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SPT IgE

• SPT data from Verstege A, 2005
• 95 positive challenge with
• Hen egg 13mm
• Cows milk 12.5mm
• IgE data from Mehl A, 2004

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Specific IgE testing
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Specific IgE testing

• If a likely allergen type is not clear from
  history taking, specific IgE testing will not
  usually help.
• This means panels of allergens are not usually
  helpful
• Except
• Persistent aero allergen problems
• Nuts
• Exploring cross reactions, eg latex, OAS

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Challenge testing Indications

• Used in allergy
• When tests unreliable eg wheat
• Occupational asthma
• Usually when low prior probability
• Used in non allergic situations
• Salicylates
• Other drug

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Challenge testing Process

• Admit for all drugs
• Placebo controlled, double blind structure
• Consent
• Written structure with agreed endpoints
• FEV1
• BP
• MCT

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Mast cell tryptase

• Anaphylaxis
• Peaks at 15 mins 2 hrs
• Persists for up to 3 days
• Ideal to do testing up to about 12 hours
• Other causes of mast cell degranulation also
  incease MCT
• MCT persistently elevated in mastocytosis

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Other tests

• Vega testing
• Kinesiology

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Important distinction Patch testing
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Common diagnostic pitfallsUrticaria

• Chronic urticaria is rarely allergic
• Infection
• Drugs
• Auto immune disease
• Thyroid
• Connective tissue disease
• Anti mast cell antibody

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Allergy prevention

• Allergen exposure reduction
• Absolute reduction possible necessary for
• Antibiotics and other drugs
• Latex
• Relative reduction possible, without proven
  benefit in
• House dust mite
• Pollen
• Risk assessment
• Nuts
• Other foods
• Animals

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Allergy prevention

• Desensitization
• Insect venom
• Safe and often indicated
• SCIT 90 efficacy
• Grass pollen
• Relatively safe and sometimes indicated
• SCIT 90 efficacy
• SLIT 60 efficacy

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Allergy prevention

• Preventative drugs
• Topical steroids
• Best regarded as preventative drugs
• Assiduous use and good delivery required
• Cromoglycate
• Mainly ophthalmic allergy
• Omalazumab
• NICE approval for refractory allergic asthma

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Allergy Treatment

• Adrenaline
• 500mg im in hospital 0.5ml 11,000
• 300mg im at home
• May not work
• With poor technique
• in obese
• on b blockers
• 500mg slow iv in hospital 5ml 110,000

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Allergy Treatment

• Antihistamines
• Can work rapidly eg chewed chlorpheniramine
• Minimal effects on isolated asthma
• Care with driving
• Leukotriene antagonists

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Conclusions

• Patients with severe acute allergy
• Check mast cell tryptase
• Same sample can be used to measure specific IgE
• Referral recommended
• Patients with chronic allergy symptoms
• Please refer, although we may suggest
  investigations that can be done locally