Unless obtaining written consent is a legal requirement (and in most countries it is not), consent for an HIV test can be given verbally, as with other tests. European guidelines state that test rates increase if written consent is not required.
In the vast majority of cases, the pre-test discussion will be brief. However, if a patient seems particularly anxious about having a test, they should be given the opportunity to express their concerns. They may be fearful about the potential impact of HIV, and the stigma that can be associated with it, on different aspects of their life. They may also be worried about the confidentiality of the test result. Clear information and reassurance (where possible) should be offered. If the patient remains reluctant to test, you can repeat the offer at their next appointment after they have had time to consider, or it may be helpful to arrange for them to see a counsellor at the local HIV service.