some of the most important parasites are in the bowel wall, not in the stool.
I did PCR testing with metramex also, they missed very very important deadly parasite that they told were negative on these...
Exact reason for this is unclear. Possibly and very likely the parasite load in stool is so low that even PCR misses it. Have in mind some of these parasites live in the bowl wall, this is also the most dangerous parasites as they attack the tissue and can give symptoms all around the body. Several of the best books tell they are often undetectable on these type of tests. We know they live in the bowel wall, this is why they give such horrible symptoms, they attack the body.
Several of the best books says some of these parasites, especially after acute phase, when entering chronic phase these are no longer found in stool but in bowel wall. It is well known from literature stool tests will miss out on these. Still lots and lots of doctors and labs claim they can rule them out based on lab tests that very easy will miss out on them.
An alternative possible explanation (but it seems one for a long time already have the explanation, they live in the bowel wall) is due to the fact that for several of these parasites there are many many sub-types. Very likely also PCR is developed based on some subtypes and will not pick up other subtypes. But anyway there is likely very very very little of them (I am thinking of the very seripous bug E. Histolytica) in the samples Metrametix test especially in chronically sick people. Histolytica lives in the bowel wall and will very often missed on PCR and Stool antigen tests also. We do not know 100% reason for this, but we know this. There could be even several reasons they miss out in many cases. Of course no test method is 100%....but these type of tests seems to often miss bugs like Histolytica. And yes literature seems to have know this for very very long time. They live in the bowel wall! One need to do mucus scrapings from bowel wall, and very trained personal need to do this.
If I had trusted these PCR tests I would have been doomed. Luckily I met a world leading parasitologist that actually did what all the best books says one need to do to rule these out. Mucus scrapings of bowel wall is a must!