A blood serum "PCR" test indicates the presence, or lack of same, of yeast in the bloodstream. Referred to as "systemic" candida, meaning it's moving throughout your bodily systems. Yeast really gets around, living comfortably in the bowels, female places, and I'd bet even places like ear wax, nasal pbeautyages, etc. But I believe it has no business being in the bloodstream. This would suggest it's getting past an impaired intestinal lining "leaky gut" or some other avenue. The liver would normally filter this stuff out, but is often compromised or overwhelmed during bad GI candida infections. While holistic physicians might often suggest herbs for GI candida, even they will often say "Bring out the big guns" and subscribe an Antibiotic if diagnosed as systemic. Once in the bloodstream, yeast can manifest itself in all sorts of symptoms with each organ it comes across (including the brain), probably helping explain things like irritability, depression, brain fog, etc.