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Selection of skin tests in asthma
Brit.
J. Dis.
Chest
(1973)
67,
SELECTION
238
OF SKIN
TESTS
IN ASTHMA
0. R. MCCARTHY* The London
Chest Hospital
prick tests were carried out on London to see how frequently positive allergens and to find out what is the be required to identify patients with selection of allergens. SKIN
Patients
a group of asthmatic patients living in reactions occur to a selection of different minimum number of allergens likely to positive reactions to at least one of the
and Methods
The patients were among those attending a chest clinic and a hospital in northeast London. They all were considered to have asthma because of spirometritally variable airways obstruction. Fifty patients seen consecutively were selected and had skin tests as part of the investigation of their illness. There were 12 females and 38 males. Their ages ranged from 7 to 68 years. In addition to asthma, 21 patients had rhinitis, 2 had hay fever, 5 had eczema and 2 had chronic bronchitis (Medical Research Council 1965). Skin tests were carried out by the prick method (Pepys 1972). A drop of fluid containing the allergen was placed on the forearm; the skin was pricked through the fluid (with a No. 20 disposable needle) as superficially as possible to minimize non-specific reactions. The tests were read after IO minutes, and any weal bigger than the control test reaction was accepted as positive. The 18 allergens used are shown in Table I. TABLE
I.
THE
NUMBER
Allergen Candida
albicans
Dry rot Asfiergi1Lu.s Alternaria
fumigates
Yeast Grass pollens Spring flowers Tree Shrub * Present address: Medway
OF
PATIENTS WITH ALLERGEN
Positive reaction
A
POSITIVE
SKIN
TEST
TO
Positive reaction
Allergen
I
Milk
4
2
Egg Fish Nuts Cat fur Dog hair House hair Horse dust
22
4 3 26 : 6
Dermatofagoides
Hospital,
Gillingham,
(Received for fiublicntion
Kent. March
1973)
3 21 20
farinae
8 40 38
EACH
SKIN
TESTS
IN
239
ASTHMA
All patients had been asked to stop tablets or medicine containing or antihistamine at least one day before the tests.
ephedrine
Results Fifty patients were tested; 7 gave no skin reactions to any of the 18 allergens (Table I). Of the 43 with positive reactions 40 reacted to house dust, 38 to Dermatofagoides farinae, 26 to grass pollens, 21 to cat fur and 20 to dog hair. No other allergen gave positive reactions in more than 8 patients (see Table I). Thus, testing with a single allergen identified 40 of the 43 patients with positive skin test reactions. The results using 2 allergens would identify nearly all the patients with positive skin tests (Table 2). TABLE
z.
NUMBER
Pair
OF
of allergens
POSITIVE REACTIONS TO PAIRS OF ALLERGENS
Positive reactions
D. farinae Grass pollens House dust D. farinae
42
House dust Grass pollens House dust Cat fur House dust Dog hair
47
Pair
ONE
OR
of allergens
D. farinae Cat fur D. farinae Dog hair Grass pollens Dog hair Grass pollens Cat fur
4’
40
BOTH
OF
DIFFERENT
Positive reactions
40 40 32 3’
40
The patients who showed positive reactions to house dust overlapped with those showing positives to D. farinae. Three with positive house dust reactions were negative to D. farinae, and one with a positive D. farinae reaction was negative to house dust. and the largest weal did not exceed No systemic reactions occurred, 20 mm in diameter. One patient had a Fran01 tablet (I I mg ephedrine, I 20 mg theophylline, 8 mg phenobarbitone) and another had Iso-Bronchisan (15 mg isoprenaline, 25 mg ephedrine, I 30 mg theophylline) , both about 3 hours before skin testing. Nevertheless, these patients had 3 and 7 positive skin tests respectively. Discussion A positive skin test alone is not proof of that allergen being responsible for the patient’s symptoms. Symptom-free individuals, particularly if there is a family history of allergy, may have positive skin tests. The response to a nasal or bronchial challenge would show the relevance of such a reaction but this is seldom needed and is not without danger. Nevertheless, skin tests have a worthwhile though restricted place in the
MCCARTHY
5?P
management of patients with asthma. Thus, they help to differentiate between extrinsic and intrinsic asthma; this is useful because disodium cromoglycate seems more effective in extrinsic asthma, whereas patients with intrinsic asthma often need corticosteroid drugs. Furthermore, identification of specific allergens which precipitate attacks may be helpful when grass pollen or the house dust mite is responsible because there is evidence that hyposensitization can be beneficial in these circumstances (Frankland & Augustin 1954; Smith 1971). However, hyposensitization to other allergens has not been shown to be effective. Also, attempts to avoid exposure are seldom successful because the causative allergen is likely to be ubiquitous. The results of this study suggest that adequate information can be obtained by three skin pricks, using a control, D. farinae and grass pollen allergens. To these might be added Aspergillus fumigatus because of the importance of identifying allergic bronchopulmonary aspergillosis. These tests can be carried out very quickly and are practical for out-patient clinics. An important difference between the use of the limited and the full range of tests might be in the identification of atopic subjects. One practical clinical definition of atopy has been suggested as ‘those patients with clinical allergy (for example asthma, eczema or rhinitis) who react to more than one different group of allergens in a standardized range of prick skin tests’ (Turner Warwick 197 I). Clearly, the smaller the number of allergens used the greater the possibility of not recognizing all the patients with atopy. However, very few will be missed if there is a low incidence of hypersensitivity to the omitted allergens. Summary In a group of 50 asthmatic patients seen consecutively skin prick tests to 18 allergens were carried out. Forty-three patients has positive skin tests. The allergens D. farinae and grass pollens, or both, gave positive reactions in 42 patients. It is suggested that as few as four skin pricks-a control, D. farinae, grass pollens and Aspergillw fumigatus-give adequate information, and are practical for use in out-patient clinics. ACKNOWLEDGEMENT
I wish patients
to thank the physicians of the and for their encouragement.
London
Chest
Hospital
for
allowing
me
to examine
their
REFERENCES
FRANKLAND, A. W. Lance&
& AUGUSTIN, R.
(1954)
Prophylaxis
of summer
hay-fever
and
asthma.
i, 1055.
MEDICAL RESEARCH COUNCIL (1965)
Definition
6 774. PEPYS, J. (1972) Skin tests for immediate SMITH, A. P. (1971) Hyposensitisation asthma induced by house dust. Br. TURNER WARWICK, M. (1971) Provolring
and
classification
of chronic
bronchitis.
type I allergic reactions. Proc. R. Sac. Med., with Dermatobhagoides pteronyssinus antigen: med. J., iv, 204. factors in asthma. Br. 3. Dis. Chest, 65, I.
Lance& 65, 271. trial in
J. Dis.
Chest
(1973)
67,
SELECTION
238
OF SKIN
TESTS
IN ASTHMA
0. R. MCCARTHY* The London
Chest Hospital
prick tests were carried out on London to see how frequently positive allergens and to find out what is the be required to identify patients with selection of allergens. SKIN
Patients
a group of asthmatic patients living in reactions occur to a selection of different minimum number of allergens likely to positive reactions to at least one of the
and Methods
The patients were among those attending a chest clinic and a hospital in northeast London. They all were considered to have asthma because of spirometritally variable airways obstruction. Fifty patients seen consecutively were selected and had skin tests as part of the investigation of their illness. There were 12 females and 38 males. Their ages ranged from 7 to 68 years. In addition to asthma, 21 patients had rhinitis, 2 had hay fever, 5 had eczema and 2 had chronic bronchitis (Medical Research Council 1965). Skin tests were carried out by the prick method (Pepys 1972). A drop of fluid containing the allergen was placed on the forearm; the skin was pricked through the fluid (with a No. 20 disposable needle) as superficially as possible to minimize non-specific reactions. The tests were read after IO minutes, and any weal bigger than the control test reaction was accepted as positive. The 18 allergens used are shown in Table I. TABLE
I.
THE
NUMBER
Allergen Candida
albicans
Dry rot Asfiergi1Lu.s Alternaria
fumigates
Yeast Grass pollens Spring flowers Tree Shrub * Present address: Medway
OF
PATIENTS WITH ALLERGEN
Positive reaction
A
POSITIVE
SKIN
TEST
TO
Positive reaction
Allergen
I
Milk
4
2
Egg Fish Nuts Cat fur Dog hair House hair Horse dust
22
4 3 26 : 6
Dermatofagoides
Hospital,
Gillingham,
(Received for fiublicntion
Kent. March
1973)
3 21 20
farinae
8 40 38
EACH
SKIN
TESTS
IN
239
ASTHMA
All patients had been asked to stop tablets or medicine containing or antihistamine at least one day before the tests.
ephedrine
Results Fifty patients were tested; 7 gave no skin reactions to any of the 18 allergens (Table I). Of the 43 with positive reactions 40 reacted to house dust, 38 to Dermatofagoides farinae, 26 to grass pollens, 21 to cat fur and 20 to dog hair. No other allergen gave positive reactions in more than 8 patients (see Table I). Thus, testing with a single allergen identified 40 of the 43 patients with positive skin test reactions. The results using 2 allergens would identify nearly all the patients with positive skin tests (Table 2). TABLE
z.
NUMBER
Pair
OF
of allergens
POSITIVE REACTIONS TO PAIRS OF ALLERGENS
Positive reactions
D. farinae Grass pollens House dust D. farinae
42
House dust Grass pollens House dust Cat fur House dust Dog hair
47
Pair
ONE
OR
of allergens
D. farinae Cat fur D. farinae Dog hair Grass pollens Dog hair Grass pollens Cat fur
4’
40
BOTH
OF
DIFFERENT
Positive reactions
40 40 32 3’
40
The patients who showed positive reactions to house dust overlapped with those showing positives to D. farinae. Three with positive house dust reactions were negative to D. farinae, and one with a positive D. farinae reaction was negative to house dust. and the largest weal did not exceed No systemic reactions occurred, 20 mm in diameter. One patient had a Fran01 tablet (I I mg ephedrine, I 20 mg theophylline, 8 mg phenobarbitone) and another had Iso-Bronchisan (15 mg isoprenaline, 25 mg ephedrine, I 30 mg theophylline) , both about 3 hours before skin testing. Nevertheless, these patients had 3 and 7 positive skin tests respectively. Discussion A positive skin test alone is not proof of that allergen being responsible for the patient’s symptoms. Symptom-free individuals, particularly if there is a family history of allergy, may have positive skin tests. The response to a nasal or bronchial challenge would show the relevance of such a reaction but this is seldom needed and is not without danger. Nevertheless, skin tests have a worthwhile though restricted place in the
MCCARTHY
5?P
management of patients with asthma. Thus, they help to differentiate between extrinsic and intrinsic asthma; this is useful because disodium cromoglycate seems more effective in extrinsic asthma, whereas patients with intrinsic asthma often need corticosteroid drugs. Furthermore, identification of specific allergens which precipitate attacks may be helpful when grass pollen or the house dust mite is responsible because there is evidence that hyposensitization can be beneficial in these circumstances (Frankland & Augustin 1954; Smith 1971). However, hyposensitization to other allergens has not been shown to be effective. Also, attempts to avoid exposure are seldom successful because the causative allergen is likely to be ubiquitous. The results of this study suggest that adequate information can be obtained by three skin pricks, using a control, D. farinae and grass pollen allergens. To these might be added Aspergillus fumigatus because of the importance of identifying allergic bronchopulmonary aspergillosis. These tests can be carried out very quickly and are practical for out-patient clinics. An important difference between the use of the limited and the full range of tests might be in the identification of atopic subjects. One practical clinical definition of atopy has been suggested as ‘those patients with clinical allergy (for example asthma, eczema or rhinitis) who react to more than one different group of allergens in a standardized range of prick skin tests’ (Turner Warwick 197 I). Clearly, the smaller the number of allergens used the greater the possibility of not recognizing all the patients with atopy. However, very few will be missed if there is a low incidence of hypersensitivity to the omitted allergens. Summary In a group of 50 asthmatic patients seen consecutively skin prick tests to 18 allergens were carried out. Forty-three patients has positive skin tests. The allergens D. farinae and grass pollens, or both, gave positive reactions in 42 patients. It is suggested that as few as four skin pricks-a control, D. farinae, grass pollens and Aspergillw fumigatus-give adequate information, and are practical for use in out-patient clinics. ACKNOWLEDGEMENT
I wish patients
to thank the physicians of the and for their encouragement.
London
Chest
Hospital
for
allowing
me
to examine
their
REFERENCES
FRANKLAND, A. W. Lance&
& AUGUSTIN, R.
(1954)
Prophylaxis
of summer
hay-fever
and
asthma.
i, 1055.
MEDICAL RESEARCH COUNCIL (1965)
Definition
6 774. PEPYS, J. (1972) Skin tests for immediate SMITH, A. P. (1971) Hyposensitisation asthma induced by house dust. Br. TURNER WARWICK, M. (1971) Provolring
and
classification
of chronic
bronchitis.
type I allergic reactions. Proc. R. Sac. Med., with Dermatobhagoides pteronyssinus antigen: med. J., iv, 204. factors in asthma. Br. 3. Dis. Chest, 65, I.
Lance& 65, 271. trial in