It is very important when getting tested for Lyme disease to have these tests done at a reputable laboratory that is well set up for the testing of Lyme disease and it's many co-infections.
Once you have your results, it then becomes VERY important to have a doctor who is Lyme literate and well versed in all things Lyme... There are many factors which can affect the results, so a Lyme literate medical doctor (LLMD) is a MUST in this next step of interpreting your results.
A list of reasons has been compiled from the Lyme Disease Foundation and the Lyme Alliance by Melissa Kaplan, 2003:
Nine Reasons for False Negative Lyme Disease Blood Test Results
From the Lyme Disease Foundation brochure, Frequently Asked Questions About Lyme Disease.
Also, Tom Grier of Lyme Alliance gives Reasons Why A Seronegative Test Result Might Occur.
See this link:
http://www.anapsid.org/lyme/lymeseroneg.html