IGeneX labs, in Palo Alto CA. They have a website.
Your doc is right, IGeneX has a test that looks in your blood for DNA of the Lyme bacteria, instead of (like Western blot and ELISA tests) that look for your immune system's reaction to Lyme bacteria. That is, IGeneX tests look for direct evidence of Lyme rather than indirect evidence.
Like in a mystery story: finding the bad guy's boots is better than finding just his muddy footprints.
IGeneX has a website with short explanations of what their tests do.