Patch testing - 深圳市普威国际检测认证有限公司

A patch test is a skin testing method used to detect contact allergens. It is primarily employed in the diagnosis of allergic contact dermatitis, eczema, and other allergic skin conditions caused by exposure to external substances. The test helps identify which specific substances a patient is allergic to, thereby guiding avoidance measures to prevent future allergic episodes.

Test Principle

Substances that may cause allergic reactions (allergens) are prepared at specific concentrations as solutions, ointments, or in their original form, and are applied to the patient's skin (typically the back or the flexor aspect of the upper arm) using patch test chambers. After a defined period, the skin reaction is observed to determine whether the patient is allergic to the tested substance.

Test Procedure

Preparation Phase:

Select common allergens (e.g., cosmetic ingredients, metals, dyes, preservatives, rubber products, fragrances, etc.), or specific substances suspected based on the patient's history.
Prepare allergens at appropriate concentrations (to avoid skin irritation) and place them into the wells of the patch test chambers.

Patch Application:

Cleanse the test site (typically the upper back) and avoid applying any skincare products or medications beforehand.
Apply the patch test chambers containing the allergens onto the skin and secure them with adhesive tape, ensuring close contact with the skin.

Observation Timing:

Typically, the patch test chambers are removed at 48 hours after application, with the first skin reaction assessment conducted at that time.
A follow-up reading is performed at 72 or 96 hours (some delayed reactions may only manifest during this phase).

Result Interpretation

Results are graded according to the degree of skin reaction:

Negative (-): no reaction of any kind;
Doubtful (+/-): faint erythema only;
Weak positive (+): erythema, mild edema, or scattered small papules;
Strong positive (++): marked erythema, edema, papules, and vesicles;
Extreme positive (+++): severe erythema, edema, bullae, and erosion.

Precautions

During the test period, avoid strenuous exercise, excessive sweating, and bathing to prevent the patch test chambers from detaching or affecting the results.
Do not scratch the test site. If significant itching, pain, or swelling occurs, inform the physician promptly.
For individuals experiencing an acute dermatitis flare, those with widespread skin damage, or those who are highly sensitive to multiple substances, the test should be performed with caution or deferred.
Test results must be interpreted by a physician in conjunction with the patient's clinical history; some positive reactions may represent irritation rather than true allergy.

Indications

Individuals suspected of skin allergy resulting from contact with substances such as cosmetics, metal jewelry, textile dyes, etc.
Patients with chronic eczema or contact dermatitis who require identification of specific allergens to prevent recurrence.

Patch testing is an important clinical tool for diagnosing contact allergy and should be performed by a physician in a professional healthcare setting to ensure accurate and safe results.