Exactly - it could indicate another infection. If you have Lyme symptoms though, that is what the doctor is supposed to be going by, not the test results. Even the CDC says this much:
"Lyme disease is diagnosed based on symptoms, physical findings (e.g., rash), and the possibility of exposure to infected ticks. Laboratory testing is helpful if used correctly and performed with validated methods."
www.cdc.gov/lyme/And this article was recently brought to my attention (thanks P!) :
georgialymedisease.org/yahoo_site_admin/assets/docs/ws_-Volkman_1_comments_IDSA_guidelines.100215315.pdf(note - this is a pdf) The first few pages go into detail about
why the testing is so messed up and why it's so inaccurate for so many.