ALLSA - Flow Diagram for Allergy Diagnostic Work Up

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Allergy Diagnostic Work-Up

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Flow Diagram for Allergy Diagnostic Work-Up

A A thorough history and clinical examination remains the cornerstones of a reliable allergy diagnosis. Diagnostic tests are to be used as adjuncts.  Top

B By using the clinical information provided by A;
(i) differentiate between allergy and clinical conditions that mimic allergy; and
(ii) place the possible cause of the patient's allergy into one or more of the 4 groups, based on the route of entry of the allergen(s) into the body.   Top

C Airborne allergens usually cause respiratory symptoms (rhinitis and/or asthma) and/or conjunctivitis; these can be either perennial or seasonal.  Top

D Skin-prick testing (SPT). Experience is needed for performance and interpretation of SPT reactions. The Bayer inhalant SPT panel consists of a positive and negative control, and the following inhalent allergens: cat, dog, mixed feathers, house-dust mite, mixed grass, Bermuda grass, maize pollen and mixed trees.  Top

SPT is contraindicated under the following circumstances:
1. Skin: dermatographism and eczema (SPT may be difficult to interpret in very darkly pigmented skin).
2. Allergens: dangerous allergens (penicillin, horse, venoms); unreliable allergens (especially FOODS and moulds)
3. Medication: patients who are taking antihistamines and other drugs that suppress the SPT reactions.
4. Age: although it is more difficult in children under 3 years of age, it is possible to perform SPT on children as young as 6 months.   Top

E Serum samples should consist of 2 ml of serum. Sera are held for 2 weeks at the laboratory, should individual RAST testing be needed after a positive Phadiatop, total IgE or RAST multi-allergen screening test.  Top

F Specific immunotherapy (SIT). It is recommended that a RAST for the specific allergen be performed prior to immunotherapy, even with a concordant clinical history and SPT results. This is especially true for grasses where the RAST will assist in identifying the important grass allergen of the SPT grass mixture, which should be included in the immunotherapy vaccine.  Top

G The Phadiatop inhalant screening test is a YES/NO inhalant allergen screening test (grass-, weed- and tree-pollens, mould spores, epithelia and house dust mites). It is not influenced by age, race, parasites or drugs, is equal to or greater than 93% sensitive and equal to or greater than 96% specific. It is superior to total IgE measurement for the detection of inhalant allergy.  Top

H RAST inhalant mixed-allergen screening tests tests for a group of related inhalant allergens grass-, weed- and tree pollens, mould spores, epithelia, mixed feathers and house dust). A positive result should ideally be followed up with the individual RAST(s) for the individual relevant allergen(s). A negative result excludes all the individual relevant allergens, so obviating the need to test for many single allergens. Alternatively, individual RAST allergen testing can be requested, especially if individual allergen are strongly suspected or with a smallish RAST panel (dotted arrow-line on diagram).

RAST and Phadiatop are registered trademarks belonging to Pharmacia Diagnostics of Uppsala, Sweden.  Top

I RASTs for individual inhalant allergens are available for a wide range of airborne allergens. A positive result confirms with a great degree of reliability the identity of the causative allergen(s).  Top

J A negative RAST result is also very reliable, but if there is doubt, the test should be repeated 1 month later, especially if there is a variable/increasing allergen load (e.g. pollen of a particular tree coming into season).  Top

K RASTs specific for bee venom and penicillin are most commonly requested, though true incidence is actually far less than generally supposed. SPT is STRONGLY contraindicated. Send blood 3-4 weeks after the 'inoculation' for the RAST to the suspected individual allergen.  Top

L IgE-medicated allergy to foods is only one of several types of adverse reactions to food. To test for other types of food hypersensitivity (e.g. food additives), challenge testing will be necessary.  Top

M For infants and children less than 2-3 years of age, the diet is normally restricted to on a small range potential allergenic foods. For children older than 3 and adults, as the diet is more varied, other allergens must also be additionally considered in the diagnostic work-up.  Top

N The RAST Paediatric Food Mix is one of the ingestant panels in the range of RAST ingestant mixed allergen screening tests and covers the foods commonly found in the <2 years age group diet (egg white, milk, wheat, soya, peanut and fish).  Top

O The other ingestant panels of the RAST ingestant mixed-allergen screening tests consist of nuts (e.g. peanut), seafood (e.g. fish, shrimp), cereals (e.g. wheat, maize), fruit (e g. banana, orange, apple, peach), meat (e.g. chicken, beef, pork), spice (e g. basil, fennel, seed, ginger, anise) and vegetable (e.g. tomato, spinach, cabbage, paprika).  Top

P RASTS for the more common individual ingestant allergens (see N & 0) are available from the laboratory; testing for other suspected allergens can be arranged.  Top

Q Allergen avoidance is the optimal therapy for ingestant allergy and it is thus absolutely necessary to identify reliably each individual offending food allergen.  Top

R A value of total IgE > mean +1 standard deviation for age indicates allergy, but many circumstances limit its usefulness (e.g. wider and higher reference range in black and coloured population groups render total IgE of little practical value, massive increases in IgE levels in the presence of parasitic infestation mask elevation due to an allergy and with a small allergic 'target organ', such as in allergic rhinitis, the elevation in total IgE may be moderate/absent, giving apparent false-negative indication). Reliability is approximately 50-60%.  Top

S Provocation or challenge tests are reserved only for special cases where the clinical diagnosis is still not confident. They should be conducted by experienced clinicians in controlled circumstances with emergency resuscitation equipment immediately available.  Top

T Approximately 95% of contact dermatitis is NOT IgE mediated, but is due to a chemical hypersensitivity. A patch test by a dermatologist for the suspected causative agent(s) is recommended.   Top


A	A thorough history and clinical examination remains the cornerstones of a reliable allergy diagnosis. Diagnostic tests are to be used as adjuncts. Top

B	By using the clinical information provided by A; (i) differentiate between allergy and clinical conditions that mimic allergy; and (ii) place the possible cause of the patient's allergy into one or more of the 4 groups, based on the route of entry of the allergen(s) into the body. Top

C	Airborne allergens usually cause respiratory symptoms (rhinitis and/or asthma) and/or conjunctivitis; these can be either perennial or seasonal. Top

D	Skin-prick testing (SPT). Experience is needed for performance and interpretation of SPT reactions. The Bayer inhalant SPT panel consists of a positive and negative control, and the following inhalent allergens: cat, dog, mixed feathers, house-dust mite, mixed grass, Bermuda grass, maize pollen and mixed trees. Top

	SPT is contraindicated under the following circumstances: 1. Skin: dermatographism and eczema (SPT may be difficult to interpret in very darkly pigmented skin). 2. Allergens: dangerous allergens (penicillin, horse, venoms); unreliable allergens (especially FOODS and moulds) 3. Medication: patients who are taking antihistamines and other drugs that suppress the SPT reactions. 4. Age: although it is more difficult in children under 3 years of age, it is possible to perform SPT on children as young as 6 months. Top

E	Serum samples should consist of 2 ml of serum. Sera are held for 2 weeks at the laboratory, should individual RAST testing be needed after a positive Phadiatop, total IgE or RAST multi-allergen screening test. Top

F	Specific immunotherapy (SIT). It is recommended that a RAST for the specific allergen be performed prior to immunotherapy, even with a concordant clinical history and SPT results. This is especially true for grasses where the RAST will assist in identifying the important grass allergen of the SPT grass mixture, which should be included in the immunotherapy vaccine. Top

G	The Phadiatop inhalant screening test is a YES/NO inhalant allergen screening test (grass-, weed- and tree-pollens, mould spores, epithelia and house dust mites). It is not influenced by age, race, parasites or drugs, is equal to or greater than 93% sensitive and equal to or greater than 96% specific. It is superior to total IgE measurement for the detection of inhalant allergy. Top

H	RAST inhalant mixed-allergen screening tests tests for a group of related inhalant allergens grass-, weed- and tree pollens, mould spores, epithelia, mixed feathers and house dust). A positive result should ideally be followed up with the individual RAST(s) for the individual relevant allergen(s). A negative result excludes all the individual relevant allergens, so obviating the need to test for many single allergens. Alternatively, individual RAST allergen testing can be requested, especially if individual allergen are strongly suspected or with a smallish RAST panel (dotted arrow-line on diagram). RAST and Phadiatop are registered trademarks belonging to Pharmacia Diagnostics of Uppsala, Sweden. Top

I	RASTs for individual inhalant allergens are available for a wide range of airborne allergens. A positive result confirms with a great degree of reliability the identity of the causative allergen(s). Top

J	A negative RAST result is also very reliable, but if there is doubt, the test should be repeated 1 month later, especially if there is a variable/increasing allergen load (e.g. pollen of a particular tree coming into season). Top

K	RASTs specific for bee venom and penicillin are most commonly requested, though true incidence is actually far less than generally supposed. SPT is STRONGLY contraindicated. Send blood 3-4 weeks after the 'inoculation' for the RAST to the suspected individual allergen. Top

L	IgE-medicated allergy to foods is only one of several types of adverse reactions to food. To test for other types of food hypersensitivity (e.g. food additives), challenge testing will be necessary. Top

M	For infants and children less than 2-3 years of age, the diet is normally restricted to on a small range potential allergenic foods. For children older than 3 and adults, as the diet is more varied, other allergens must also be additionally considered in the diagnostic work-up. Top

N	The RAST Paediatric Food Mix is one of the ingestant panels in the range of RAST ingestant mixed allergen screening tests and covers the foods commonly found in the <2 years age group diet (egg white, milk, wheat, soya, peanut and fish). Top

O	The other ingestant panels of the RAST ingestant mixed-allergen screening tests consist of nuts (e.g. peanut), seafood (e.g. fish, shrimp), cereals (e.g. wheat, maize), fruit (e g. banana, orange, apple, peach), meat (e.g. chicken, beef, pork), spice (e g. basil, fennel, seed, ginger, anise) and vegetable (e.g. tomato, spinach, cabbage, paprika). Top

P	RASTS for the more common individual ingestant allergens (see N & 0) are available from the laboratory; testing for other suspected allergens can be arranged. Top

Q	Allergen avoidance is the optimal therapy for ingestant allergy and it is thus absolutely necessary to identify reliably each individual offending food allergen. Top

R	A value of total IgE > mean +1 standard deviation for age indicates allergy, but many circumstances limit its usefulness (e.g. wider and higher reference range in black and coloured population groups render total IgE of little practical value, massive increases in IgE levels in the presence of parasitic infestation mask elevation due to an allergy and with a small allergic 'target organ', such as in allergic rhinitis, the elevation in total IgE may be moderate/absent, giving apparent false-negative indication). Reliability is approximately 50-60%. Top

S	Provocation or challenge tests are reserved only for special cases where the clinical diagnosis is still not confident. They should be conducted by experienced clinicians in controlled circumstances with emergency resuscitation equipment immediately available. Top

T	Approximately 95% of contact dermatitis is NOT IgE mediated, but is due to a chemical hypersensitivity. A patch test by a dermatologist for the suspected causative agent(s) is recommended. Top