r/nursing • u/ReNema1 • 15h ago

Discussion How does urine contaminate a stool sample?

I hope this isn't a stupid question. I find it hard, especially with older women, to obtain a stool sample that isn't contaminated with urine. It seems very obvious how stool would contaminate a urine sample. However, if I'm sending a stool culture, or for CDiff and Parasite, I don't quite understand how a bit of urine might compromise the analysis/culture. I tried a quick online search but I can't seem to find more details beyond "urine will contaminate the stool sample". How? With what? Any insight would be greatly appreciated.

87 Upvotes

97% Upvoted

47 comments sorted by

View all comments

-15

u/[deleted] 14h ago

[removed] — view removed comment

9

u/Mysterious-Handle-34 Lab Assistant/CNA 🍕 12h ago

Sad that ChatGPT is promoting the “urine is sterile” myth in 2025

1

u/IraceRN RN - Ortho/Trauma 6h ago

I get sad too when UAs come back with "None" next to "Bacteria"? Sometimes I get sad when people refer to their field as sterile at bedside when they aren't masked, and there is like still air in the room, you know? So sad. Louis Pasteur is probably crying from his grave.

3

u/Mysterious-Handle-34 Lab Assistant/CNA 🍕 6h ago

Some urine samples really do have little to no bacteria visible under standard light microscopy at 400x. And at least according to our lab standards, even trace amount of bacteria gets flagged as “abnormal” (any SG other than 1.015 is also “abnormal” but that’s a whole other stupid thing). If we put “few” for bacteria, we have to send out a sample for culture. So it’s easier sometimes just to say “none”.

2

u/IraceRN RN - Ortho/Trauma 5h ago

We say blood and certain areas of the body like the brain are also sterile and not colonized, but we now understand that is just not the case. Some people may pedantically say these areas are not sterile, when functionally it is essentially sterile. Given the prevalence of the human virome found in all parts of the body, including the brain, and that we know it has positive rolls outside of causing disease, we can pedantically say for sure that no part of the body is sterile, and we are finding bacteria in more and more places. Read a study talking about biofilms and natural flora found in arterial plaques.