Scratch Test


Skin of the arm or forehand is cleansed and a series of superficial abrasion/scratches of about 1A 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 / abrased) and removed after 15-20 minutes from the skin, and reactions occuring at the test site are observed an interpreted on the basis of comparison with control tests. Control tests are made with diluents of the allergenic principle.

Intracutaneous Tests


About 0.02 ml of each of the sterile allergenic extracts is introduced into the skin by a syring 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 control
10-20 mm


2+ 3 times more
than the control
3+ 4 times more than
the control
4+ 5 times more than
the control
20-30 mm More than 30mm
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 tests are carried out for following:

1. Grasses: Such as Sorghum, Cenchrus, Cynoden andPennisetum.

2. Trees: Morus, Putranjiva, Cassia Siamea, Eucalyptus,Kigelia, Melia, Prosopis, Salvadora and Ricinus.

3. Weeds: Ageraturm, Adhatoda, Asphodelons, Brassica,Argemone, Chenopodium Album, Xanthium, Parthenium,Dodonea, Artemesia, Amaranthus and Parthenium.

4. Fungi: Mucor, Phoma, Alternaria, Candida, AspergillusFumigatus, cladodosporium, Hehninthosporium.

5. Danders: Cat, Horse, Dog.

6. Dusts: Wheat dust, House dust, Paper dust, Cotton dust.