First, it depends on what type of test you're using.
We used to use a different type of ELISA first, followed by the Western blot, and now we have a C6 ELISA first, which is a better tool. However, then we were still following it up with the Western blot, and if the Western blot was negative, we were saying that you didn't have Lyme.
As Ralph was saying, the C6 by itself should be diagnostic of Lyme disease, and in parallel we could do an ELISpot to pick up the people that C6 misses.