Intracutaneous test

Further test for the diagnosis of an IgE-mediated allergic reaction of the immediate type ( type I allergy) with sterilized, diluted test solutions on the skin; to be performed in case of negative or doubtful rubbing test, scratch test and prick test.

In addition, the test is also used for the diagnosis of late type allergic reactions of the tuberculin type (type IV reaction) and of the granulomatous type (type V reaction) (see also under recall antigens)

• Using a fine cannula (insulin cannula), about 0.03-0.05 ml of the allergen solution is injected strictly intracutaneously on the forearm flexion side (more rarely on the back), resulting in a small wheal of 3 mm diameter. A positive control (0.01% Histamine Lsg.) and a negative control (0.9% NaCl Lsg.) should be tested to exclude false negative and false positive test reactions.
• For type I allergens the urticarial reaction is read after 20 minutes. According to the diameter of the wheal and reflex erythema in comparison to the positive and negative control, the respective test reactions are evaluated semi-quantitatively from 0 to ++++, analogous to the prick test.
• The reading of the allergic late type reactions (tuberculin or granuloma type) is performed according to the course of the immunological reaction after 48 and 72 hours or after 3-4 weeks.

Local and systemic allergic type I reactions can occur (especially in case of improper testing as well as high sensitization and undiluted test solutions, e.g. drugs and insect venoms!) See below provocation test.

With the implementation of European directives into national law, test solutions for allergy diagnostics are "drugs in the sense of the German Drug Law (AMG)". They therefore require approval as a prerequisite for distribution in Germany. The high expenditure for the acquisition of this approval, with simultaneous increase of costs for quality control, has led to the fact that since 17.1.1992 (!) no test allergen has been newly approved. It is to be expected that this test procedure, which has been established for decades, will completely disappear from the diagnostic repertoire.

1. Darsow U et al (2003) Atopic patch test. Atopic eczema and allergy. dermatologist 54: 930-936
2. Klimek L et al (2015) Intracutaneous testing is disappearing. Allergo J 24: 46
3. Ring J (1988) Applied allergology. 2nd edition. MMW Publishing House, Munich