If the allergist, after receiving the information from the referring physician and from the patient, thinks that there is a need to test allergy to penicillins, then he will refer the patient to the allergy clinic in the hospital where a penicillin test can be performed.
Once in the hospital, the test begins by skin prick testing different components of penicillins. If there is no response, diluted penicillins are injected under the skin in several rounds, each round using a more concentrated material until a skin reaction occurs, if at all.
Between each round there is an observation period of around 15 minutes. If there is no response to the skin injections even in the most concentrated round, the next step is a penicillin challenge, in which the patient will receive a small amount of oral penicillins, under controlled conditions, so that if there is a reaction he will immediately receive the necessary medical treatment. In the absence of a reaction, the dose of penicillins will be escalated until a therapeutic dose is reached. The patient will be monitored for two hours after the last dose. If still there is no reaction, the patient is released with a summary that explains that there was no reaction to penicillins during the surveillance period. However, to be sure that there is no allergy to penicillins, we will have to wait for another week because there are delayed reactions that may occur even several days after the challenge. However, dangerous reactions occur during the observation period, so that no dangerous response is expected at home, if at all.
If after a week there is still no reaction, we can rule out penicillin allergy.
If at any stage there is a reaction, so the patient will be diagnosed as allergic to penicillins.
The reason to test penicillins only in a hospital setting is that there is a possibility of a dangerous reaction and therefore the patient must be tested where all the appropriate infrastructure to handle a reaction is available. In addition, the whole test sometimes takes some hours between the skin tests and the penicillin challenge. Therefore, the appropriate framework to test is in the hospital day care.