Covid, is an antibody test enough to avoid the third dose of vaccine?

Tests that measure the antibodies against Covid, which are used more and more frequently, almost necessary in anticipation of a third dose of vaccine to be inoculated to everyone and not only, as is the case now, to over 60, frail and health workers. But can these tests, with the level of antibodies they measure, really represent a passport to immunity? The US FDA (US government body that deals with the regulation of food and pharmaceutical products) has reached a negative conclusion.