Epicutaneous test

Primary, largely standardised test for the diagnosis of a late allergic reaction of the eczema type (see below Allergy), especially in allergic contact dermatitis. For the composition of the standard series for adults and children, see table.

The frequency of allergic contact eczema in children is reported to be between 5-20%. Children < 6 years of age should only be selectively tested if there is a strong suspicion of allergic contact dermatitis, > 12 years the test can be performed according to the recommendations for adults.

According to the recommendations of the German Contact Allergy Group (DKG, valid since 1.1.2014), the standard test series for adults is composed as follows ( cited in Mahler V. 2015)

Test substances Test concentrations Test bases

1. Potassium dichromate 0,5 % Vaseline (Vas.)
2. Thiuram mix 1 % Vas.
3. Cobalt (II) chloride, 6*H20 1 % Vas.
4. Peru balsam 25 % Vas.
5. Colophony 20 % Vas.
6. N-Isopropyl-N'-phenyl-p -phenylenediamine 0,1 % Vas.
7. Wool wax alcohols 30 % Vas.
8. Mercapto mix without MTB 1 % Vas.
9. Epoxy resin 1 % Vas.
10. Nickel (II) sulphate 5 % Vas.
11. Methylisothiazolinone 0,05 % Aqu.
12. Formaldehyde 1 % Aqu.
13. fragrance mix 8 % Vas. (see remark)
14. Turpentine 10% Vas.
15. (chlorine)-methyliso- thiazolinone (MCI/MI) 100 ppm Aqu.
16. Paraben mix 16 % Vas.
17. Cetylstearyl alcohol 20 % Vas.
18. Zinc diethyldithiocarbamate 1 % Vas.
19. Dibromodicyanobutane(Methyldibromo Glut.) 0,2 % Vas.
20. Propolis 10 % Vas.
21. Sandalwood oil 10 % Vas.
22. Compositae Mix II 5 % Vas.
23. Mercaptobenzothiazole 1 % Vas
24. Lyral 5% Vas.
25. Iodopropynyl butylcarbamate 0,2 % Vas.
26. Fragrance Mix II 14 % Vas. (see remark)
27. Sodium lauryl sulphate (SLS) 0,25 % Aqu.
28. Ylang-ylang (I + II) oil 10 % Vas.
29. Jasmine absolute 5 % Vas.

Note: The listed test substances are available in the epicutaneous test series" Fragrance Mix" and "Fragrance Mix II".

According to the recommendations of the German Contact Allergy Group (DKG) the standard epicutaneous test for children consists of the following substances:

1. nickel sulphate
2. Thiuram mix
3. Rosin
4. Mercaptobenzothiazole
5. Fragrance mix I
6. Fragrance Mix II
7. Mercapto Mix
8. Bufexamac
9. Dibromdicyanobutane
10. Chloromethylisothiazolinone
11. Neomycin
12. Composite Mix
13. p-tert. butylphenol formaldehyde resin (only for shoe exposure)
14. Potassium dichromate (only for shoe exposure)
15. Wool wax alcohols (only for skin care products)
16. Disperse blue mix (only for clothing)
17. Paraphenylenediamine (only for henna tattoos).

The application time should be limited to 24 hours, further readings according to the recommendations for adults after 48 and 72 hours.

To avoid a toxic skin reaction, the allergen is highly diluted in an indifferent base (usually Vaseline) and applied (glued) to the healthy skin of the back in small test chambers made of aluminum (e.g. Finn Chambers), thin film (True-Test) or cellulose. The test reaction is regularly read after 48 hours and 72 hours, occasionally also after 96 hours. If clinical relevance is questionable, a so-called repeated open application test (ROAT) or use-use test can also be carried out, in which the allergen is tested daily on the inside of the upper arm for 1 week. Another option for clarifying clinical relevance is open testing in loco.

The following are evaluated:

• - (no reaction = negative)
• ? (questionable; only erythema, no infiltrate)
• + (single positive reaction; only erythema, possibly with a small infiltrate; possibly discrete papules)
• ++ (double positive reaction; erythema and papules, infiltrate, vesicles)
• +++ (triple positive reaction; erythema, infiltrate, confluent vesicles)
• ++++ (quadruple positive reaction; eroded vesicles; classified by many allergists as a triple positive reaction)
• IR (irritant-toxic reaction; soap effect, vesicles, blister, necrosis)
• nt (not tested; allergen contained in a test block but not tested)
• f (follicular reaction; they are to be assigned to the reactions in question in the evaluation).

The reaction dynamics of the epicutaneous test can be included in the evaluation. A crescendo or plateau pattern is more indicative of the allergic type, a decrescendo pattern is more indicative of the irritant type. In the case of late reactions, which occur for the first time about 10-14 days after application of the epicutaneous test, an ("iatrogenic") sensitization by the test should be considered.

Positive reactions to structurally related substances may be cross-reactions.

If positive reactions (> 5) occur to chemically unrelated substances, this may be an expression of an individually increased sensitivity to the contact allergy. Alternatively, if there are numerous positive reactions, an angry back/excited skin syndrome should always be considered. In such a case, many of the morphologically positive (+ to +++) reactions should be interpreted as false positives.

If there is no allergic reaction in the epicutaneous test despite clear anamnestic or clinical indications of the presence of sensitization, this gives rise to the suspicion of a "false negative" reaction. This may be due to the test method (allergen concentration too low, unsuitable vehicle, inadequate occlusion, reading sequence too short) or to the patient's reduced immunoreactivity (e.g. due to topical or systemic medication or UV light). In the case of false positive reactions, for example in the context of an "excited skin syndrome", or if false negative reactions are suspected, the testing of the individual substances should be repeated at a later date, if possible after 2 months. Other procedures such as application tests (e.g. ROAT) can help to clarify the sensitization in the hands of experienced examiners.

False positive epicutaneous test reactions (possibly more than 5) in the sense of a so-called angry back due to a massive test reaction to a strong contact allergen with a hematogenous scattering reaction into other (negative) test areas can occur if the epicutaneous test is performed too early on skin that is still eczematized or in the case of an acute eczema flare. On the other hand, false negative test reactions are to be expected with iatrogenic T-cell suppression (internal steroid therapy, antihistamines, UVA therapy, etc.).

Silent sensitization: Positive epicutaneous test result without evidence of current or past allergic contact dermatitis.

After reading an epicutaneous test, the clinical relevance of the type IV sensitization present must always be assessed. All information should then be documented for the patient in an allergy passport. It makes sense to indicate the clinical relevance with reference to the allergen in the passport. The clinical relevance can be indicated using the so-called COADEX index. This comprises the most important, practice-relevant criteria.

The tear-off epicutaneous test can be regarded as a modification. This is carried out, for example, to detect a persistent clinical suspicion of a contact allergy if the epicutaneous test is negative.

Pregnancy and epicutaneous testing: According to the guideline, epicutaneous testing should not be carried out during pregnancy (possible permeation of allergens).

The authorities intend to assess the epicutaneous test in future in accordance with the guidelines of the German Ordinance on Medicinal Products and Active Substances ( AMWHV), also known as "Good Manufacturing Practice (GMP)". This means that ingredients of care products such as body lotions, for example, may only be tested under GMP quality.

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