Skin test

"A skin test should be done before taking penicillin and cephalosporin" is a household common sense. But is this common sense really completely correct? In the first half of this year, the National Health Commission issued a milestone document - "Guidelines for Skin Testing of β-Lactam Antimicrobial Drugs (2021 Edition)", which clearly stated the skin testing issues of widely used penicillin and cephalosporin antibiotics. What are the important changes in the new version of the principles? Is a skin test required before the use of cephalosporins? What precautions should be taken before a skin test? Today, the pharmacist will take you to learn about skin tests.

1. In what situations is a skin test necessary?

1. Before using penicillin antibiotics (such as ×× penicillin, ×× cillin), a penicillin skin test is required regardless of the different routes of administration, such as oral, intravenous or intramuscular injection.
2. Routine skin testing is not recommended before using cephalosporins. Skin testing is only required in the following situations:

① Patients who have experienced allergic reactions such as urticaria, angioedema, bronchospasm, anaphylactic shock, etc. within a few minutes to an hour after using penicillin or cephalosporin.

② The drug instructions stipulate that a skin test is required.

2. Is the skin test prediction accurate?

Penicillin itself and its metabolites, degradation products, and side chain structures can all trigger allergic reactions, and a complete penicillin skin test reagent should contain the above substances. Even with a complete skin test reagent, the positive predictive value of a penicillin skin test is only 50% and the negative predictive value is 70% to 97% through a complete and standardized skin test diagnostic method. The penicillin skin test reagents available in my country only contain penicillin itself, which is even less predictive. The decomposition products of cephalosporins have not yet been fully identified, and there is no evidence-based medical evidence to support the predictive value of skin tests. Therefore, skin testing is only one of the risk prevention measures. In comparison, reducing the risk of allergic reactions is more about finding out whether the child has a clear history of allergies, close observation during medication, and timely treatment in the event of severe allergic reactions.

3. Why should the routine skin test for cephalosporins be cancelled?

The decomposition products of cephalosporins have not yet been fully identified, and skin testing is just a long-standing custom. In fact, the correlation between a positive cephalosporin skin test and an allergic reaction is not high. In other words, people with a positive skin test do not necessarily experience allergic symptoms when using cephalosporins, and people with a negative skin test do not guarantee that they will not experience allergic symptoms when using cephalosporins. Therefore, it is meaningless to conduct routine skin tests for cephalosporins.

4. Do children with allergic diseases need to undergo skin tests when using cephalosporins?

For children with allergic diseases such as allergic rhinitis, allergic asthma, atopic dermatitis, and food allergies, the chance of cephalosporin allergy is no higher than that of the general population, and there is no need for routine skin tests before using cephalosporins. However, if such children have an allergic reaction after taking the medicine, the symptoms may be more severe. Parents should strengthen observation after taking the medicine. If you feel unwell, please inform the medical staff in time. For children with asthma that is poorly controlled or in the acute attack stage, once a severe allergic reaction occurs, the symptoms will be more severe. Therefore, skin tests are best performed during the asthma control period.

5. The child’s skin test was positive before. Is it necessary to conduct a skin test before using cephalosporin?

Pharmacists here would like to remind parents to clarify a concept: a positive skin test does not mean "allergy". It can only be called "allergy" if a severe allergic reaction occurs during the previous use of penicillin or cephalosporin. Therefore, children with a positive skin test in the past do not need to undergo routine skin tests before using cephalosporin. When parents explain the allergy history to the doctor, they must explain the situation in detail.

6. Which drugs will affect the results of skin tests?

Antiallergic drugs, glucocorticoids and other drugs can inhibit skin reactions, resulting in negative skin test results for children who may be allergic. Therefore, if your child is using these drugs in the table, they should be discontinued if the condition permits, to reduce interference with the skin test. If there is a history of taking related drugs in the past week, please inform the doctor in time.

At the same time, it should be noted that beta-blockers (such as propranolol) and angiotensin-converting enzyme inhibitors (such as cardopril) can affect the treatment of severe allergic reactions. Patients with high risk factors for severe allergic reactions should stop taking these drugs for at least 24 hours before skin testing.

The "Guidelines for Skin Testing of β-lactam Antimicrobial Drugs" provide a clear basis for standardizing skin testing of β-lactam antibiotics. Canceling routine cephalosporin skin testing will not only avoid the waste of medical resources, but will also greatly reduce the pain of children, shorten the time of medical treatment, and further reduce the burden on parents. I hope you can have a correct understanding of skin testing through this article. Compared with the results of skin tests, children's medical history and allergy history are more instructive for the prevention and control of medication risks. Therefore, parents should pay more attention to their children in daily life, provide detailed medical and personal history when seeing a doctor, and help doctors develop reasonable medication plans. Please work with us to build a great wall of children's health.