What is a baseline series of patch test allergens?
Patch tests are used to identify the cause of contact allergic dermatitis. Standard or baseline 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/baseline 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 amount of a petrolatum-based allergen is carefully squeezed into a chamber. Liquid allergen solutions are dropped onto the filter paper placed in the test chamber. Two or three completed patches are fixed to the skin of the upper back; in some cases, an 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 baseline series?
The chemicals in the baseline series depend on which one is being used. The European Baseline 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
| Allergen | Concentration % (w/w) in petrolatum | Source of dermatitis | Positive reaction |
|---|---|---|---|
| Potassium dichromate | 0.5 | 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 and Vioform) | 5.0 | Clioquinol (antibacterial) |  |
| Colophonium | 20.0 | Rosin and 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 butyl phenol-formaldehyde resin (adhesive) |  |
| Mercaptobenzothiazole | 2.0 | Rubber antioxidant |  |
| Formaldehyde | 2.0 in water | Formaldehyde and 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 and 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) | 0.02 in water | Isothiazolinone (preservative) |  |
| Budesonide | 0.01 | Topical corticosteroid |  |
| Tixocortol pivalate | 0.1 | Topical corticosteroid |  |
| Methyldibromo glutaronitrile | 0.5 | Formaldehyde-releasing preservative |  |
| Methylisothiazolinone | 0.2 in water | Preservative |  |
| Fragrance mix II | 14 | Fragrance and perfume |  |
| Textile dye mix | 6.6 | Disperse textile dyes |  |
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:
| Allergen | Concentration mg/cm2 in petrolatum | Source of dermatitis | Positive reaction |
|---|---|---|---|
| Carba mix | 0.25 | Rubber antioxidant |  |
| Ethylenediamine dihydrochloride | 0.050 | Ethylenediamine (preservative) |  |
| Thiomersal | 0.0070 | Thiomersal (mercurial preservative) |  |
| Diazolidinyl urea | 0.55 | Formaldehyde-releasing preservative |  |
| Imidazolidinyl urea | 0.60 | Imidazolidinyl urea (preservative) |  |
| Hydrocortisone-17-butyrate | 0.02 | Topical corticosteroid |  |
| 2-Bromo-2-nitropropane-l,3-diol (Bronopol) | 0.5 | Formaldehyde-releasing preservative |  |
| Bacitracin | 0.6 | Antibiotic (topical medication) |  |
| Disperse Blue 106/124 Mix | 0.05 | Textile dye |  |
| Parthelonid (feverfew) | 0.003 | Compositae plant |  |
| Sodium thiosulfate (gold) | 0.075 | Metal see Gold |  |
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.
| Allergen | 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 | A 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 and perfume |  |
| Propylene glycol | 30.0 in water | A vehicle in medications, cosmetics, foods. | |
| 2-Hydroxy-4-methoxybenzophenone (Benzophenone 3) | 10.0 | Sunscreen |  |
| 4-Chloro-3,5-xylenol (PCMX) | 1.0 | Preservative | |
| Ethyleneurea, melamine formaldehyde mix | 0.1 | 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 | An acrylic monomer used in adhesives and coatings |  |
| Glyceryl monothioglycolate (GMTG) | 1.0 | Acid perming solution |  |
| Toluenesulfonamide formaldehyde resin | 10.0 | A synthetic resin in lacquers and adhesives (nail cosmetics) |  |
| 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) | 4.5 | Formaldehyde type of textile resin | |
| Cocamidopropylbetaine | 1.0 | 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 baseline 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 (eg, 'hairdressers series', dental series') or other risk factors ('shoe series', 'cosmetic series').
Atopy patch tests are sometimes undertaken in patients with atopic dermatitis where there is suspicion of exacerbation by a type 1 allergen such as a food or house dust mite.