If asthma is caused or, at least, suspected by some allergen, try to find out as to which of the allergens is the real causative factor and also what and when symptoms surfaced first; in which seasons symptoms aggravated. It is quite necessary to take a detailed history of the patient; taking into account the said points. One would be expected to undergo the following tests with the advise of a specialist.
In order to detect presence of reagins (antibodies) which are present in the skin and blood, skin tests are called for. Union of antibody in the skin, with its corresponding antigen applied in the skin tests, causes the release either of histamine-like or histamine substance by the tissues and results in redness and a weal around the site.
Skin tests are performed with extracts of pollens, moulds, dusts, etc. While concluding or carrying out such tests, it must be ensured that extracts are processed in most appropriate method, are neither old, active or potent, have no pathogenic micro-organisms in them and have minimal amount of any antigen. The results will be more accurate and precise if the antigen extract retains more natural characteristics. When the extract is ready (after sterilization and stardization), skin tests are carried out either by :
□ Scratch Test or
□ Intracutaneous test
Skin of the arm or forehand is cleansed and a series of superficial abrasion/scratches of about lA cm long are made either of the said parts. It should be ensured that scratches or abrasions are not made deep lest bleeding takes places.
Now allergence extracts are applied over the sight (which has been scratched or abrased) and removed after 15-20 minutes from the skin, and reactions occuring at the test site are observed and interpreted on the basis of comparison with control tests. Control tests are made with diluents of the allergenic principle.
About 0.02 ml of each of the sterile allergenic extracts is introduced into the skin by a syringe but reactions, due to application of this technique, are often quite larger than the ones obtained from the scratch test and the results obtained may also vary. It is necessary to carry out such intracutaneous tests with much care and precision otherwise, in most cases, allergic reactions are most likely to surface though such tests are not painful and can be easily carried out with children who soon lose their apprehension.
These skin tests are graded from 0-4 + depending upon the degree of redness and swelling produced. If there is a significant positive reaction, the same must correspond to and match with the clinical history of the patient recorded earlier.
GRADING OF SKIN TESTS
Grade, size of weal and size of redness can be determined from the following table:
Grade Size of Weal Size of Redness
0 Same as control Same as control
1 + 2 times more
than the control 10-20 mm
2+ 3 times more
than the control 20-30 mm
3+ 4 times more than More than
the control 30 mm
4+ 5 times more than
the control More than 40 mm
Normally negative reactions point out to absence of antibody against the tested allergen but other considerations (such as use of weak, inadequate or deteriorated extracts) can account for negative reactions/absence of antibody. Skin teste are carried out for following :
□ Grasses : Such as Sorghum, Cenchrus, Cynoden and Pennisetum.
□ Trees : Morus, Putranjiva, Cassia Siamea, Eucalyptus, Kigelia, Melia, Prosopis, Salvadora and Ricinus.
□ Weeds : Ageraturm, Adhatoda, Asphodelons, Brassica, Argemone, Chenopodium Album, Xanthium, Parthenium, Dodonea, Artemesia, Amaranthus and Parthenium.
□ Fungi : Mucor, Phoma, Alternaria, Candida, Aspergillus Fumigatus, cladodosporium, Helminthosporium.
□ Danders : Cat, Horse, Dog.
□ Dusts : Wheat dust, House dust, Paper dust, Cotton dust.