Final answer:
If redness and swelling were found around the test area when performing a predisposition test, the correct step to take is to stop the service.
Step-by-step explanation:
If redness and swelling were found around the test area when performing a predisposition test, the correct step to take is A. Stop the service. Redness and swelling indicate a reaction to the test, which could potentially worsen if the service is continued. It is important to prioritize the client's health and safety, so stopping the service is the appropriate course of action.