Physical examination and history taking are important in establishing the presence of contact dermatitis and its possible causes. However, the history and examination alone cannot exclude the possibility of contact dermatitis. That is why contact allergen testing is indicated unless the dermatitis is obviously irritant in nature.

Important clues to the nature of the dermatitis can be obtained by noting the location of the skin inflammation. Inflammation on the legs, hands, arms, and other areas can provide important information as to the likelihood of an allergic or irritant origin. Morphologic nuances, including the presence of vesicles, erythema, pustules, round or irregular patches, and edema, can also be important in differential diagnosis.

Physical examination coupled with detailed history taking can often form the basis of a preliminary diagnosis of ACD. However, only contact allergen testing can definitively establish the presence of ACD and identify the offending allergens.

Contact allergen testing has a positive impact for the majority of patients in terms of identification of allergens to avoid; education about allergic and irritant factors, protective measures, and/or therapeutic expectations; and improvement of the dermatitis. Accurate identification of the offending allergen(s) through contact allergen testing allows patients to prevent recurrence of the condition mainly by avoiding contact with the identified allergens.

Patch testing augments the diagnostic process. Often, the contact allergen test response is the crucial piece of information that allows for the early identification of the offending allergen(s) and confirmation of a diagnosis of ACD. If physician and patient can determine how contact was made to the allergenic substance, the patient can then take appropriate action to avoid exposure to the allergen and, if possible, to substitute non-allergenic agents.

There are instances when a positive test response is indicative of an allergy not to the specific allergen tested but to a related, cross-reactive substance. For example, a positive test reaction to p-Phenylenediamine may not only incriminate the dye itself, but it may also alert the physician to the possibility that a group of immunochemically related substances, such as local anesthetics that have an amino group in the para position, may need to be investigated as potential allergens.

Negative test results to contact allergen testing are also important to the diagnostic process, by helping to rule out the most common allergens as the source of the persistent eczematous condition, guiding the physician's search for possible causes.

TRUE TEST™ (Allergen Patch Test) is a ready-to-use contact allergen test for the differential diagnosis and management of persistent eczematous conditions. Routine early contact allergen testing with TRUE Test™ can help resolve persistent eczema faster and more economically.

TRUE Test™ also may be used adjunctively to determine the presence of a contact hypersensitivity component in other long-standing and stubborn cases of dermatologic diseases, such as atopic dermatitis, seborrheic dermatitis, hypostatic eczema, dyshidrotic eczema, stasis dermatitis, and psoriasis.

When in-depth investigation beyond the TRUE Test™ allergens is required, other more flexible testing procedures may be employed.

It's extremely difficult to make an immediate diagnosis of contact dermatitis. The initial site of the dermatitis and the pattern of spread are the most important features and are of more value than the nature of the eruption itself. The most common problems of differential diagnosis are with atopic dermatitis, stasis dermatitis, and hand dermatitis, but seborrheic dermatitis, nummular dermatitis, cellulites, urticaria, mycotic infections, pompholyx, and even psoriasis may be simulated.

Allergic contact dermatitis should be suspected:
when an eczema is not improving as expected despite
treatment
when exposed to a possible allergen or irritant areas
of skin are affected
in eczema of sudden onset, with no past history
in eczema of unusual pattern or distribution
when there has been contact with a known allergen
in persistent eruptions involving hands, feet, face, ears,
or legs

When to Patch Test
to confirm a diagnosis of Allergic Contact Dermatitis
to screen for allergy in eczema that is hard to diagnose
or treat