I thought it was odd that my PCR results show HHV 6A and 6B as 'not detected'.
PCR detects viral infection in the blood, which you will have during an acute infection or a reactivated infection. But in enterovirus-associated ME/CFS, the enterovirus infections are known to be in the tissues (eg muscle and gut tissues), which is why PCR on the blood for enterovirus is often negative.
In Dr Lerner's
abortive herpesvirus infection theory of ME/CFS, it is also believed that the herpesvirus infection resides in the tissues, not the blood, hence possibly why blood PCR for herpesviruses can be negative.
Antibody tests do not measure the viral infection directly, but measure the immune response to the infection, so these antibody tests can detect infections hidden in the tissues.
Which is why some ME/CFS specialist doctors believe that the high antibody titers often found in ME/CFS are an indication of an infection in the tissues (and in the case of enterovirus, if you perform a PCR on a muscle tissue biopsy, rather than the blood, you often get a positive result, proving that there is infection in the tissues).
But other researchers think these high titers may not reflect any infection, but just be due to immune dysfunction. So nothing is clearcut.
But the bottom line is that ME/CFS doctors who treat ME/CFS infections indicated by high titers (with antivirals or immunomodulators) do get good results, which have been published in clinical trial studies. So for practical purposes in a clinical setting, these high titers are useful indicators of which treatment to administer.