I was recommended to take the sample to the lab on monday because if the lab personnel works only during the week the sample will be examined shortly after. Putting it in the fridge is certainly better in case you have a bm in the evening and then you need to drop it off only the next day. I would not worry about the fixative. Anyway, in my opinion stool tests are not reliable: imagine having a big bm, taking one small scoop for the test, and the stuff they need to look for stays in the rest of the bm flushed down. Plus from the small scoop you send off, maybe only a very small amount is examined, so again, it is a huge hit or miss. I have been to a gastro doc today at the hospital, who said that 1 stool is enough to see if you have parasites. So you see how they really don't know anything. I also told him i have had a Tapeworm infection, but he said it was of no relevance.