Skin Prick Testing

Allergopharma provides test solutions for skin prick testing, intracutaneous 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, feathers, 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 intracutaneous test solutions and challenge test solutions may have to be increased.

Procedure

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.

Wheal

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.

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Intracutaneous Testing

Procedure

Intracutaneous testing is preferably performed on the back. The skin of the test site is wiped quickly with a cotton-wool swab soaked in alcohol. Using a tuberculin syringe fitted with a short ground cannula, 0.05 ml up to a maximum of 0.07 ml of the test solution is injected strictly intracutaneously. In order to avoid an overlapping of test reactions as much as possible, regular distances of 5 cm should be kept between the individual test sites. Since the skin reactivity is increased in the vicinity of the spine, a skin area of about 4 fingers wide should be left on either side of the backbone.

Negative and Positive Control

Negative and positive intracutaneous control tests have to be performed, in order to determine the individual skin test sensitivity of the patient. The test results can be read after 10 to 20 minutes. It is necessary to check the development of the skin reactions from time to time, in order to encounter possible excessive reactions in time.

Extremely Sensitive Patients

A skin prick test with a negative response to the respective allergens is the precondition for a corresponding intracutaneous test of patients who have an anamnesis of being extremely sensitized. Also, the intracutaneous test of such allergens, which are known to be very aggressive (e.g. epithelia), have to be performed after the same preparatory efforts. Moreover, in these cases the tests should be performed on the forearm and not on the back, because in case of an excessive reaction, further absorption of the allergen can be prevented by the application of a tourniquet. An additional precautional measure is to carry out a "skin titration" by means of using diluted (1:10, 1:100, 1:1000) allergen solutions, starting with the most diluted one.

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