Delayed Patch Testing Shows Varied Results

Patch testing is used to identify the substances causing allergic contact dermatitis. Patch tests are normally read on the 5th day to identify the allergens. However, when the patch tests are read beyond 5 days, additional allergens such metals and antibiotics showed a positive reaction. This research was done by Mayo clinic.

Patch Testing:

Patch testing is done by placing patches containing suspected-allergy causing substances (allergens) on the skin. The patches are removed after 46 hours. After 5 days, the skin is checked for allergic reaction. A positive reaction would mean the person is allergic to the substance. A negative reaction would mean the person is not allergic to the substance.

The Research by Mayo Clinic:

The research was conducted on 50 patients, who were tested for 170 allergens. The test was conducted on the 5th day. After this, the researchers conducted tests during 7-21 days. Compared to that of 5th day, the results of delayed testing are as follows:

  • 117 allergens showed different reactions
  • 14 allergens showed significantly higher positive reactions
  • The allergens which showed higher positive reactions included metals, antibiotics, and preservatives
  • Some allergens, such as fragrances, which were positive on day 5, showed negative reactions

According to Dr. Mark D.P. Davis, from Mayo Clinic, late patch test readings were useful in identifying reactions to topical antibiotics and metals. This research shows that delayed patch testing may be useful in identifying the allergens effectively.

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