Skin Prick Testing
Allergopharma provides test solutions for skin prick testing and challenge tests, which are used for the diagnosis of lgE mediated allergic diseases (type 1, Coombs and Gell). The Allergopharma allergen extracts are manufactured from various allergenic raw materials of biological origin, such as pollen, epithelia, moulds, mites, dusts, and foodstuffs.
The genuine allergens are isolated with careful aqueous extraction at a physiological pH value. By means of modern technological methods, these solutions are further processed; an essential step is the removal of possible irritants of low molecular weight, using diafiltration techniques.
The resulting allergen solutions (allergen bulk extract) are characterized by in-process-controls, e.g. physico-chemical and immunological analysis, resulting also in a quantification on major allergens. In a final procedure, these allergen bulk extracts are converted by freeze-drying (lyophilisation) to allergen active substances, which can be stored for a long time. For the production of test solutions, the allergen active substances are diluted with the respective diluents to obtain the required diagnostic solutions.
As a rule, the concentration of allergens in the diagnostic solutions leads to distinct allergic skin reactions, provided that the patient has been sensitized accordingly. Depending on more aggressive allergens or extremely sensitive patients, the dilution of the challenge test solutions may have to be increased.
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What happens during a skin prick test?
Skin prick tests are performed at the volar side of the forearm. In a first step the skin is marked with a pen, as shown on the right. Then one drop of each solution to be tested is put on the skin beside the respective mark.
Then the point of a prick needle or prick lancet is pushed through the drop and held against the skin for about 1 second. The shouldered skin prick test lancet just penetrates the skin allowing through a very small quantity of the solution.
Negative and Positive Control
Control tests are performed at the top and at the bottom of the skin test row, in order to determine the individual skin test sensitivity of the patient:
- Negative control test with physiological saline
- Positive control with a histamine solution.
The test results can be read after a period of 10 to 20 minutes. Nevertheless, the development of the skin reactions should be observed in the meantime. A pale yellow wheal (oedema) surrounded by a red flare (erythema) is a positive test result. In order to evaluate the test results, the skin reaction to the histamine solution is to be taken into account, e.g. the sizes of the wheal and the red flare.