Asthma, Hayfever, Eczema and Food Allergy – Investigating the Allergic Patient – Page 1

INTRODUCTION

Identification of the allergen responsible for the patient’s symptoms is the cornerstone of allergy management. The availability of a wide range of tests calls for an educated and cost effective selection of the most appropriate investigation. This chapter outlines a practical and streamlined approach to the investigation of the allergic patient.

Investigation of the allergic patient can be divided into five components:

 

1. A detailed history and physical examination.
2. Evaluation of the patient’s environment.
3. Confirmation of the presence of atopy.
4. Identification of the specific allergens causing the symptoms.
5. Monitoring the effects of allergic inflammation on the patient and the effects of treatment and allergen avoidance on the inflammatory response.

 

A flow diagram which incorporates and summarises much of what is described in the ensuing sections guiding the clinician through the special investigations is given in Appendix I(a) with the accompanying text to explain the various parts of the flow diagram in Appendix 1(b) (Ref.1).

 

 

1. History and Physical Examination

Index

In no other medical disease is the history more important. Without a thorough history one cannot appropriately investigate the patient. A check form for history taking is given in Appendix 1(a) page 170. Explanatory details of the important components in the history are given in Appendix 1(b) page 172 (Ref.1). Particular attention should be given to the presenting symptoms, the family history, a history of atopy in infancy, the patient’s geographical location, his living and work environment, hobbies, sports, pets, dietary preferences, effort tolerance, sleep patterns and drug usage. Physical examination should include a general examination looking for pallor, allergic facies, allergic salute, dark rings under the eyes, and assessing height and weight. One then proceeds to examination of the main target organs of the Allergic diseases: the upper airways, the ears, the pharynx, the nose, the eyes, the chest, and the skin. A basic assessment of lung function should include a peak expiratory flow rate (PEFR) and Vitalograph measurements of forced vital capacity (FVC) and forced expiratory volume (FEV1). Normal PEFR values for height are included in Appendix II, page 181. A table of normal values of FVC, FEV1, FEF 25-75 and PEFR for American white and black males and females is given in Appendix III(a-d), page 182. Where the diagnosis of asthma is in doubt an exercise test (Appendix IV, page 190) or a histamine challenge test (Appendix V, page 192), may be performed. A chest radiograph is usually advisable at the first assessment and radiological studies of paranasal sinuses and the postnasal space are often helpful if the history suggests paranasal pathology. Physical examination should also include an assessment of hearing and effort tolerance.

 

 

Index

[ Handbook ]



Investigating the Allergic Patient
Page 1

Written by Prof. PC Potter and Dr C Buys

 





Page 1

INTRODUCTION 1. The History and Physical Examination 2. Evaluation of the Patient’s Environment a) House dust Mite Analysis b) Detection of Pollen and Mould Allergens i.) Regional Pollen and Mould Counts ii.) Home Air Sampling iii.) Mould Plate Cultures 3. Identification of the Atopic Patient a.) Cord Blood IgE b.) Total IgE c.) The Phadiatop Test

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4. Identification of the Causative Allergen by measurement of Allergen Specific IgE a.) In Vivo Tests Skin Prick Tests b.) In Vitro Tests i.) The Radio-Allergo-Sorbent Technique (RAST) ii.) RAST Mixed-Allergen Tests iii.) RAST Tests for Individual Allergens Pollen allergy Mould allergy Food allergy Diagnosis of Venom Allergy Diagnosis of Drug Allergy

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5. Monitoring Allergic Inflammation 1. The Total Eosinophil Count 2. Nasal Eosinophils 3. Eosinophil Cationic Protein 4. Mast Cell Tryptase 5. Histamine Assays 6. CAST Assays 7. Allergy Cytokine Assays 8. Immunoglobulin Levels 9. Antibodies to the IgE Receptor 10. Blocking Antibodies References

INTRODUCTION




Identification of the allergen responsible for the patient’s symptoms is the cornerstone of allergy management. The availability of a wide range of tests calls for an educated and cost effective selection of the most appropriate investigation. This chapter outlines a practical and streamlined approach to the investigation of the allergic patient.

Investigation of the allergic patient can be divided into five components:

 

1. A detailed history and physical examination.
2. Evaluation of the patient’s environment.
3. Confirmation of the presence of atopy.
4. Identification of the specific allergens causing the symptoms.
5. Monitoring the effects of allergic inflammation on the patient and the effects of treatment and allergen avoidance on the inflammatory response.

 

A flow diagram which incorporates and summarises much of what is described in the ensuing sections guiding the clinician through the special investigations is given in Appendix I(a) with the accompanying text to explain the various parts of the flow diagram in Appendix 1(b) (Ref.1).

 

 




1. History and Physical Examination

Index

In no other medical disease is the history more important. Without a thorough history one cannot appropriately investigate the patient. A check form for history taking is given in Appendix 1(a) page 170. Explanatory details of the important components in the history are given in Appendix 1(b) page 172 (Ref.1). Particular attention should be given to the presenting symptoms, the family history, a history of atopy in infancy, the patient’s geographical location, his living and work environment, hobbies, sports, pets, dietary preferences, effort tolerance, sleep patterns and drug usage. Physical examination should include a general examination looking for pallor, allergic facies, allergic salute, dark rings under the eyes, and assessing height and weight. One then proceeds to examination of the main target organs of the Allergic diseases: the upper airways, the ears, the pharynx, the nose, the eyes, the chest, and the skin. A basic assessment of lung function should include a peak expiratory flow rate (PEFR) and Vitalograph measurements of forced vital capacity (FVC) and forced expiratory volume (FEV1). Normal PEFR values for height are included in Appendix II, page 181. A table of normal values of FVC, FEV1, FEF 25-75 and PEFR for American white and black males and females is given in Appendix III(a-d), page 182. Where the diagnosis of asthma is in doubt an exercise test (Appendix IV, page 190) or a histamine challenge test (Appendix V, page 192), may be performed. A chest radiograph is usually advisable at the first assessment and radiological studies of paranasal sinuses and the postnasal space are often helpful if the history suggests paranasal pathology. Physical examination should also include an assessment of hearing and effort tolerance.

 

 




2. Evaluation of the Environment


Index

This is an important but often neglected component of the patient’s evaluation which should ideally precede the conducting of specific in vivo or in vitro tests.

While a lot of information about the patient’s indoor and outdoor environment may be obtained from the history, a physical visit by the health practitioner to the patient’s home or work may be extremely useful. Allergenic exposure of the patient may be evaluated using the following:

 







1. House dust Mite Analysis

House dust mite antigens may be detected in dust samples from the patient’s bed, carpets or floors using direct microscopy or by the Acarex test. The Acarex test measures guanine in the faeces of the house dust mite and will reliably detect high levels of house dust mite (Ref.2) but is not sensitive at lower sensitising levels of the house dust mite (Der p 1) allergens. House dust mite antigens may be accurately quantitated using the Der p 1 ELISA test (currently only available as a research test at the University of Cape Town Allergology Unit). High levels of house dust mites are found in most homes along the coast, particularly in Cape Town and Durban (Ref.2). Although mites are also found in up to 40% of homes in Soweto (Ref.3), only a few homes have very high levels. The Acarex test is probably more useful inland and on the highveld to detect those homes which have high levels of house dust mite. Dust for analysis of mite levels should be collected in a standardised way. An area of 1 m squared of the floor besides the patient’s bed and 2 m squared of the upper surface of the mattress should be vacuumed for 2 minutes into a clean paper bag. The dust samples are then sieved in the laboratory using a 0.3 mm mesh to obtain a fine dust, prior to immunochemical analysis.

 

 

2. Detection of Pollen and Mould Allergens




i.) Regional Pollen and Mould Counts

Regional pollen and mould counts are monitored nationally using the Burkard spore trap by the University of the Witwatersrand and University of Cape Town. Pollen grains of greater than 50 grams/cubic metre of air and mould spore counts of greater than 3 000 spores/cubic metre of air are believed to cause symptoms in sensitive patients. In some patients, lower pollen counts than these may induce symptoms. Pollen and mould counts only provide retrospective information. Use of the Burkard spore trap is explained in Appendix VI, on page 195.

 

Pollen calenders are practically more useful for patients who have had their allergens documented since they can institute appropriate seasonal avoidance steps based on the known flowering times of grasses, flowers and trees. These are fairly consistent from year to year. Regional pollen calenders are given in Appendix XVII, on pages 126-131. For detailed data on grass, weed and tree pollen flowering times throughout South Africa the reader is referred to the book “Pollen and Mould Allergens in Southern Africa” (Ref.4).

 

ii.) Home Air Sampling

A Burkard personal sampler is available for detection of moulds or pollens in the patient’s home living or work environment which may not be reflected on the regional counts. Home sampling is used to best advantage at specific times when the patient is known to be experiencing allergic symptoms. Home sampling should be conducted according to the manufacturer’s instructions and repeated sampling may also be informative if the results are evaluated in relation to the patient’s varying symptoms.

 

iii.) Mould Plate Cultures

Sterile mould culture plates containing Sabourauds medium placed in the patient’s home or work environment and exposed to the air in the test area for a few minutes, will grow airborne moulds. Mould plates may take up to 3 weeks to culture. Specific moulds may be identified morphologically on the plate, or by direct microscopy by an experienced mycologist. Useful Mould avoidance measures are presented in Appendix VII, on page 198.

 

 





3. Identification of the Atopic Patient
Index



a.) Cord Blood IgE

The most useful predictor of a risk for allergy is the family history. A bi-parental history of allergic disease is associated with 75% chance of allergy in the offspring. In order to delay the onset of allergic symptoms such as eczema or food allergy in infancy it is important to evaluate this risk at birth. A cord blood IgE level of greater than 0.7kU/l is associated with an increased risk of allergic symptoms. However its measurement only has a sensitivity of about 42% and it is only useful in Caucasian populations and thus of reduced predictive value in Africa.

 




b.) Total IgE

Normal values for total IgE levels are given in Appendix VIII.

Total IgE levels are useful for screening for possible allergic disease in the following situations.

 







1. In small children under the age of 3 years.
2. When parasite infestation is not common in the patient’s environment. (Parasite infestation usually results in total IgE values of greater than 400kU/l).
3. Patients with allergic bronchopulmonary Aspergillus for diagnosis and follow up.
4. In patients suspected to be sensitive to allergens other than aero-allergens e.g. for food allergy and occupational allergy (only aero-allergens are included in the Phadiatopâ test).
5. Total IgE levels are informative in patients who appear to be allergic in spite of the presence of negative specific allergy tests.




 




It is important to remember that the total IgE may well be within normal limits even in the face of a severe allergy in a small organ (e.g. the nose).

 




c.) The Phadiatopâ Test

The Phadiatop test (Pharmacia) is the most reliable laboratory test available for the screening of patients for possible allergy to inhaled allergens. The test detects specific IgE binding to common aero-allergens in a single qualitative test. The sensitivity in South African children is 100% with a specificity of 90% (Ref.5). The Phadiatop test does not detect parasite specific IgE. It should not be used in the work-up of patients with food allergy or urticaria. It should not be requested if the history points clearly to a specific inhaled allergen as the cause of the patient’s symptoms, in which case, the specific allergen should be tested for. Phadiatop tests are reported as positive or negative. A positive Phadiatop test should be followed by a panel of common allergen specific skin tests or RASTS.

 

Index

 





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4. Identification of the Causative Allergen by measurement of Allergen Specific IgE a.) In Vivo Tests Skin Prick Tests b.) In Vitro Tests i.) The Radio-Allergo-Sorbent Technique (RAST) ii.) RAST Mixed-Allergen Tests iii.) RAST Tests for Individual Allergens Pollen allergy Mould allergy Food allergy Diagnosis of Venom Allergy Diagnosis of Drug Allergy

Page 3

5. Monitoring Allergic Inflammation 1. The Total Eosinophil Count 2. Nasal Eosinophils 3. Eosinophil Cationic Protein 4. Mast Cell Tryptase 5. Histamine Assays 6. CAST Assays 7. Allergy Cytokine Assays 8. Immunoglobulin Levels 9. Antibodies to the IgE Receptor 10. Blocking Antibodies References