The Patch Test procedure is an epicutaneous diagnostic provocation test using standardized haptens (Patch Test Haptens). Patch testing is performed by applying haptens into small chambers mounted on tape (Patch Test Units) and placed onto the patient’s skin. In sensitized individuals this immune response results in an allergic contact eczema confined to the application area of the chamber on the patient’s skin (a positive patch test reaction).
Chemotechnique provides all tools required to perform patch tests the IQ way, the gold standard for diagnosing contact allergy. In order to perform a diagnostic Patch Test, two crucial components are required; Patch Test Haptens and Patch Test Units.
The hapten preparations used in patch testing should ideally be specifically developed for patch testing purposes. The Patch Test Haptens manufactured by Chemotechnique are prepared by mixing high purity fine particle ground raw material with high grade white petrolatum.
The Patch Test haptens are grouped into Series. The typical patch test screening is performed by testing a Baseline series (sometimes referred to as a standard series) alongside additional specialist series. The Baselines series contains a selection of common haptens with high prevalence in a specific region whereas specialist series contains haptens that have high prevalence in certain occupations. The combination of series should be determined by the specific patient history.
To ensure that the hapten remains in direct contact with the skin for the time required (48h) to create a standardized controlled reaction, a Patch Test Unit is needed. A Patch Test Unit is composed of sets of chambers mounted on an adhesive tape. The purpose of the patch test chambers is to provide a defined area in which the skin will be exposed to the haptens during the testing. Due to the nature of patch testing it is important that the Patch Test Units used have good occlusion to the skin and that they are made of inert materials that do not interfere with the haptens tested.
Patch testing involves a number of scheduled patient appointments within a one-week time-frame. After the test application on Day 0, two or three appointments are needed for readings. The main reading should be performed within 48h of the removal of the Patch Test Units. A delayed response reading should be performed a full week after the initial test application for haptens that may show delayed reactions.
Diagnosis of Contact Allergy when Allergic Contact Dermatitis (ACD) resulting from type IV hypersensitivity is suspected. The indication is to test all patients in whom contact allergy is suspected or needs to be ruled out, regardless of age or anatomical site of dermatitis.
Indications also include conditions that may mimic a contact allergic reaction and needs to be ruleed out, such as:
- Erythema multiforme-like
- Lichen planus-like
- Psoriasis of the hands
- Granulomatous or lymphomatoid reactions
- Worsening of pre-existing dermatitis (stasis, atopic or seborrhoeic dermatitis)
- Mucous membrane reactions (conjunctivitis, stomatitis, vulvitis)
- Discoid (nummular) eczema
- Implant reactions
- Certain drug eruptions
Do not apply hapten on patients undergoing cortisone treatment or taking other medication altering the immune system such as immunosuppressive treatment.
Do not apply hapten on a patient with a known history of severe allergic reaction (local or systemic) to the hapten in question or on patients with severe or generalized active dermatitis.
Do not apply hapten on injured skin or on test area recently exposed to ultraviolet radiation (UV).
Do not apply hapten on patients with dermatitis on the upper back area aimed for the application of patch tests or on test sites recently treated with topical corticosteroids; wait at least 1 week after treatment.Pregnancy and lactation may be a conditional contraindication as there are no data on the safety of the test for the mother and child.
Patch Test Reactions
In sensitized patients, exposure to haptens during the patch testing procedure will normally result in a miniature eczema (normal patch test reaction). In addition to the visual imprints on the skin from each chamber, a slight erythema from the frames should be visible as a sign of good occlusion. The erythema generally subsides within 30 minutes after removal of the test units. The erythema may however prevail for up to 24h or more for patients with sensitive skin. Itching at the site of application of the Patch Test Units is not uncommon; it can either be caused by a positive patch test reaction or due to tape irritation.
A strong positive reaction may result in a flare-up of an existing, or sometimes a previous, dermatitis. Such flare-up reactions usually indicate that the responsible hapten is or has been, respectively, the cause of the dermatitis.
Sensitization by patch testing is a rare but potential complication of patch testing. It is regarded as a positive patch test reaction generally 2 weeks after an initially negative response at the same patch test site. Rarely localized transient hyperpigmentation or hypopigmentation may occur. A positive patch test reaction can rarely persist for up to several weeks.
Instruct patients to report any side effects.
• Consider priming each Patch Test Hapten contained in a syringe. Priming is done by discarding a single dose from the tip of the syringe and thereby possible evaporation/degradation of the active compound is avoided. If applications are done in a sequence, there is no need to prime before each new application.
• Do apply a recommended dose of 25 μl of hapten into the IQ Ultra™ / IQ Ultimate™ patch test chambers (25 μl equals to approximately a 5 mm string of petrolatum or a single drop of liquid).
• Non-volatile haptens can be preloaded on IQ Ultra™/IQ Ultimate™ for up to two weeks if store refreigerated in an air tight bag. Volatile haptens (such as fragrances and acrylates) cannot be preloaded. These haptens must be applied to the Patch Test Unit directly before Patch Test Application. For a list of haptens that cannot be preloaded, click here.
Applying Patch Test Units on the patient
• Wiping the test site with ethanol before application is important and will improve adhesion of the Patch Test Unit on patients with oily skin. For patients with very dry or oily skin, additional reinforcing tape might be required. Consider trimming the hair on the test site before patch test application on hairy patients.
• Use the upper part of the patients back if possible. Avoid applying Patch Test Units to the midline and the scapula. Do not put any Patch Test Units under a brassiere shoulder band which can cause dislocation of the test units.
• Apply pressure with the palm of your hand for 5 seconds when applying Patch Test Units. The pressure and heat will enhance adhesion.
• Do not patch test patients undergoing cortisone treatment or taking other medication altering the immune system such as immuno-suppressive treatment.
• Do not apply hapten on patients with dermatitis on the upper back area aimed for the application of patch tests or on test sites recently treated with topical corticosteroids; wait at least 1 week after treatment.
• Do not patch test on injured skin or on a test area recently exposed to ultraviolet radiation (UV). Advise patient to protect the Patch Test Units from sunlight (UV radiation) during ongoing patch testing.
• IQ Ultra™ only: Water submersion, showers and exercise must be avoided during the patch test period.
Hapten Information sheet
Hapten information sheets are available for each hapten, explaining where the substance can be found and if there are some known synonyms of the substance. Login on the webpage and then search for the hapten of intrest. Click the button to get/download the requested Hapten Information sheet.
Patch Test Record form
Fill in the Patch Test record form of the series tested. It facilitates to keep track of your patients test results.