Not necessarily diagnostic or even definitive, the inventory (created by the famous Dr. Drew) does seem to be at least a half-reliable barometer of self-perception. Culled from the good Doctor's experience dealing with all type of celebrity washout, the inventory contains 40 items, each with two statements (A or B).
Most interesting is that the inventory does not treat narcissism as so much a complete negative as a fact of life with varying degrees of focus: exhibitionism, self-sufficiency, etc.
If you're going to take the inventory, do that first before reading the rest of my blog.