Standard series of patch test allergens

What is a standard series of patch test allergens?

Patch tests are used to identify the cause of contact allergic dermatitis. Standard series of allergens are recommended for use in everyone undergoing patch testing because these include the most common and important allergens that cause dermatitis.

The specific standard series may vary according to the locality of the patch testing centre. The European Standard Series is most commonly used in Europe and elsewhere in the world. Other series include International Standard, Belgium Standard, Finnish Standard, GIRDCA Series, Korean Standard, North American Series, North American Photopatch, Swedish Standard and Hungarian Standard.

How are the patch tests prepared?

The patch test centre may order its allergens from several manufacturers. Most chemicals are mixed in petrolatum and are supplied in a syringe. A few chemicals are dissolved in water and are supplied in a bottle. The patches consist of hypoallergenic adhesive paper with up to ten chambers. The chambers are made of metal or plastic, and are round or square.

The chemicals have been carefully tested by the manufacturers and by dermatologists to determine the most suitable concentration for testing. If too weak, some people that are allergic to the chemical will not react to the test substance (false negative). If too strong, some people that are not allergic to the chemical will have a positive irritant reaction (false positive).

A small amounts of a petrolatum-based allergen is carefully squeezed into a chamber. Liquid allergen solutions are dropped onto filter paper placed in the test chamber. Two or three completed patches are fixed to the skin of the upper back; in some cases additional hypoallergenic tape may be necessary to keep them in place. Each patch is carefully numbered or labelled so the allergen in each chamber can be correctly identified.

The patches are generally left in place for 48 hours. The dermatologist will inspect the test site after they have been removed and at least once more, a couple of days later.

Preparing the Standard Series of patch test allergens

The T.R.U.E.® test series is already prepared; the backing paper is removed and the patches are carefully applied to the patient's back.

The T.R.U.E.® Series of patch test allergens

Which chemicals are included in the standard series?

The chemicals in the standard series depend on which one is being used. The European Standard series used in 2006 is described below. Most test substances are single compounds but some of the tests are mixtures of closely-related chemicals.

European Standard Series

European Standard of patch test allergens

Test substance	Concentration % (w/w) in petrolatum	Source of dermatitis	Positive reaction
Potassium dichromate	0.3	Chrome (cement, shoes, metal)
4-Phenylenediamine base (PPD)	1.0	Hair dye
Thiuram mix	1.0	Rubber antioxidant
Neomycin sulfate	20.0	Neomycin (antibiotic)
Cobalt chloride	1.0	Cobalt (metal)
Benzocaine	5.0	Benzocaine (local anaesthetic)
Nickel sulfate	5.0	Nickel (metal, coins, jewellery)
Clioquinol (Chinoform & Vioform)	5.0	Clioquinol (antibacterial)
Colophonium	20.0	Rosin & colophony (adhesive)
Parabens mix	16.0	Parabens (preservative)
N-Isopropyl-N-phenyl-4-phenylenediamine	0.1	Rubber antioxidant, leather shoes, oils and greases
Lanolin alcohol	30.0	Wool fat
Mercapto mix	2.0	Rubber antioxidant
Epoxy resin	1.0	Epoxy resin (adhesive)
Myroxylon pereirae resin	25.0	Balsam of Peru (fragrance)
4-tert-Butylphenol formaldehyde resin	1.0	Para-tertiary butylphenol formaldehyde resin (adhesive)
Mercaptobenzothiazole	2.0	Rubber antioxidant
Formaldehyde	1.0 in water	Formaldyde & formalin (in clothing, cosmetics, household products)
Fragrance mix (cinnamic alcohol, cinnamic aldehyde, hydroxycitronellal, amylcinnamaldehyde, geraniol, eugenol, isoeugenol, oakmoss absolute)	8.0 (Sorbitan sesquioleate 5% emulsifier)	Fragrance & perfume
Sesquiterpene lactone mix (alantolactone, dehydroxosus lactone, costunolide)	0.1	Compositae allergy (daisies)
Quaternium-15 (Dowicil 200)	1.0	Quaternium-15 (preservative)
Primin	0.01	Primula obconica (plant)
Cl+Me-isothiazolinone (Kathon CG, 100 ppm)	0.01 in water	Isothiazolinone (preservative)
Budesonide	0.01	Topical corticosteroid
Tixocortol pivalate	0.1	Topical corticosteroid
Methyldibromo glutaronitrile	0.5	Formaldehyde-releasing preservative

T.R.U.E.® Test series

Compared to the European Standard Series, the T.R.U.E.® Test allergens do not include sesquiterpene lactone, primin or methyldibromo glutaronitrile. The test panels of 29 allergens include the following chemicals:

Test substance	Concentration mg/cm2 in petrolatum	Source of dermatitis	Positive reaction
Carba mix	0.25	Rubber antioxidant
Ethylenediamine dihydrochloride	0.050	Ethylenediamine (preservative)
Thiomersal	0.0080	Thiomersal (mercurial preservative)
Diazolidinyl urea	0.55	Formaldehyde-releasting preservative
Imidazolidinyl urea	0.60	Imidazolidinyl urea (preservative)
Hydrocortisone-17-butyrate		Topical corticosteroid

North American Standard Series

The North American Contact Dermatitis Group (NACDG) Standard Screening Tray includes a greater range of allergens. Unlike the European series, it does not include clioquinol or primin. Nor does it include thiomersal. Additional allergens in the NACDG series are shown below.

Test substance	Concentration % (w/w) in petrolatum	Source of dermatitis	Positive reaction
DMDM Hydantoin	1.0	Formaldehyde-releasing preservative
Bacitracin	20.0	Antibiotic
Mixed dialkyl thiourea	1.0	Rubber antioxidant, photographic fixing, resins, photocopy paper.
Glutaraldehyde	0.5	Preservative used for sterilisation, embalming, tanning leather.
2-Bromo-2-nitropropane-l,3-diol (Bronopol)	0.5	Formaldehyde-releasing preservative
Fragrance Mix II (lyral, citral, farnesol, citronellol, hyxyl cinnamic aldehyde, coumarin)	14.0	Fragrance & perfume
Propylene glycol	30.0 in water	Vehicle in medications, cosmetics, foods.
2-Hydroxy-4-methoxybenzophenone (Benzophenone 3)	3.0	Sunscreen
4-Chloro-3,5-xylenol (PCMX)	1.0	Preservative
Ethyleneurea, melamine formaldehyde mix	5.0	Formaldehyde type of textile resin
Iodopropynyl butylcarbamate (Glycasil™)	0.2	Preservative for wood, paint, cooling fluids, cosmetics.
Disperse Blue 106/124 Mix	1.0	Textile dye
Ethyl acrylate	0.3	Acrylic monomer used in adhesives and coatings
Glyceryl monothioglycolate (GMTG)	1.0	Acid perming solution
Toluenesulfonamide formaldehyde resin	10.0	Synthetic resin in lacquers and adhesives e.g. nail varnish
Methyl methacrylate	2.0	Methacrylic monomer in plastics for dentures, artificial nails
Compositae Mix	5.0	Tanacetum vulgare (ragweed), Arnica montana (arnica), Parthenolide (feverfew), Chamomilla romana (chamomile), Achillea millefolium (yarrow)
Dimethylol dihydroxyethyleneurea (Fix.CPN)	5.0	Formaldehyde type of textile resin
Cocamidopropylbetaine	5.0	Surfactant, detergent
Triamcinolone acetonide	5.0	Topical corticosteroid

International Standard Series

In comparison to the European Standard Series, the International Standard Series (2001) does not contain cobalt, benzocaine, clioquinol, parabens, N-Isopropyl-N-phenyl-4-phenylenediamine, sesquiterpene lactone, primin or tixocortol. Imidazolidinyl urea is included. An extended series has been proposed.

What about other allergens?

There are numerous other chemicals that have been reported to cause contact allergy occasionally. About 15% of patients that have positive reactions at patch testing react to an allergen that is not in the standard series. These allergens are detected using other series of allergens or individual standardised chemicals that have been selected by the dermatologist.

Several series have been developed for patients that present with dermatitis on specific sites of the body (e.g., 'face series', 'foot series'), and for those with certain occupations (e.g., 'hairdressers series', dental series') or other risk factors ('shoe series', 'cosmetic series').