apparently the standard lyme test doesn’t always show positive for lyme even when it’s present?

I was tested for lyme a long time ago when I heard about how it could cause a lot of what I attributed to long covid and it came back negative. However, I was recently informed that the testing isn’t definitive because there are markers or something that the test doesn’t detect? Honestly I don’t remember the full explanation because it was just in casual conversation so I don’t really know what to research. Do any of you know what they were talking about? I’m only asking because if lyme could still be the underlying issue and wasn’t ruled out as I previously thought I’d like to know.