Your values should look natural, as blood tests will be performed in check-up tests. If your appointment is in the morning, do not eat before 12 at night and drink very little water. If your appointment is in the afternoon, come without breakfast. Before your appointment, do not smoke for at least 12 hours and do not consume alcohol for 72 hours. For women, postpone your appointment if you are on your period. Likewise, if you are taking medication as a result of a certain illness, you should postpone your appointment.