PCR testing isn't very sensitive; that is, it misses a lot of positives because the probability of finding random bug bits in an even more random blood sample is fairly low. But if you do test positive on a PCR test, it is a true positive, whereas with antibody testing, that is not always the case. It would also seem that the bug DNA, if it is found in a random blood sample, means that the infection is fairly severe in the body, (although I don't have data to back that statement up).
As mentioned in my book, "The Lyme Disease Survival Guide", if you can't afford to do tests, performing a trial run of a treatment for a particular infection is another good way to ascertain its presence. But if you can afford the tests, consider doing them through one lab, and if the results come out negative, but you suspect Lyme and co-infections, then test again through another.
Yes, they are expensive, but performing a test every few years is worthwhile. Energetic testing is often more accurate than blood tests, but unless you have a stellar device and/or a genius practitioner to test for infections, blood tests can be a better option. Besides, testing positive for babesia and other infections through a PCR test is comforting, in a sense, because then you know the suckers were actually found in your blood. It rules out all questions of "maybe." At least for me, it did.
All this said, however, you can still test negative multiple times for an infection through PCR and antibody testing, but still have that infection active and wreaking havoc in your body. For instance, my bartonella test with both Fry and IgeneX was negative, but I wouldn't be surprised if that infection were still present in my body. Lest I be tempted by two negative tests to forget about bartonella, I have made a mental note to myself that I may yet need to treat this infection again one day.
Still, doing a test twice can sometimes reduce the probability of a false result, and for this reason, I think it is worth considering doing, if you can afford it.