Redness and swelling after skin test

I believe that many people in their lives often experience redness and swelling after skin tests. This is an allergic reaction, which means that the drug cannot be used. Because during intravenous injection, there is no guarantee whether the body can accept the drug, so it can only be determined through temporary skin tests to determine whether there will be some allergies. The degree of allergy in the skin test needs to be determined based on the following table.

Decision Analysis

1. The results of type I hypersensitivity reactions are observed within 20 to 30 minutes after antigen stimulation. The positive reaction of the prick test is mainly redness, while the positive reaction of the intradermal test is mainly wheal. The judgment criteria are shown in Table 24-2.

Table 24-2 Criteria for judging the results of rapid skin test

Intradermal prick test

- No response or less than control No response or less than control

+ Wheal 3~5mm, red halo <20mm red halo > control, ≤20nm

++ wheal 6~9mm, with redness>20mm, no wheal

+++ Wheal 10~15mm, with redness and wheal

++++ Wheal > 15 mm, erythema with pseudopodia and wheal

2. The results of type IV allergic reaction are observed within 48 to 72 hours after exposure to the antigen. The positive results of intradermal tests are mainly redness, swelling and nodules, while the positive results of patch tests are mainly redness, swelling and blisters. The judgment criteria are shown in Table 24-3.

Table 24-3 Delayed skin reaction test results criteria

Degree of reaction Intradermal test Patch test

- No response or less than control No response or less than control

+ Only redness, mild swelling, itching

++ Redness and swelling with induration Obvious redness and swelling, sometimes with erythema

+++ Redness, swelling, induration, blisters Redness, swelling with rash, blisters

++++ Bullae or (and) ulcers, redness and swelling, bullae with ulcers