Quoting queso:" if you want to test with your saved FMU do you have to refrigerate it? I got a possible faint line this ... [snip!] ... take a good pic with it. That and I have no FRER so I wanted to save the pee til its light outside and I can get another test."
This was on the peeonastick website.
37. Can I still use pee that's been sitting in a cup for several hours?
hCG (pregnancy hormone) does break down and dissipate from urine once it leaves the body. It has a half-life of 24 hours, meaning the total amount will be cut in half for every day it sits out. If you are testing very early when only a small amount of hCG is present to begin with, that half might make a difference (for example, 25 mIU/mL of hCG will be detected with any early pregnancy test. By the time that pee sits out for a day, it has only 12.5 mIU/mL left, and only a very
sensitive test may detect it.)
However, most women aren't peeing in cups and leaving it around for days; most women just want to save their FMU
(or other concentrated urine) to be used later in the day (may need to purchase an HPT, want to wait for darling dearest to get home from work, may pee in a cup out of preference and then get distracted by a toddler doing a serious number on the poor kitty before you get the chance to dip the test, etc. All very common scenarios.) A few hours is unlikely to make a serious difference in the amount of hCG in your urine, so it's fine to use older pee. Putting your pee in the fridge will also slow the breakdown of the hormone, but I will disavow all knowledge of this suggestion in the event that your husband is grossed out by its proximity to his leftover pizza.