Just an FYI, soon the instructions on the urine test will be revamped..there is alot that can 'go wrong' thus making the test results ambiguous, mostly operator error..testing too soon or too late ie outside the window of time the test will catch, using hot urine & a cold test, or test and urine too hot or too cold, flooding the well instead of one drop at a time, bacteria or mold in the urine if left out too long before use, leaving the test unrefrigerated if not used in a day or two etc. These only affect the false positives claim I'm told by the lab.
If there is no fetus there are no fetal hormones for the test to pick up...I'd be curious to know if your mare is pregant after getting a negative test result, your procedure for running the test and during what time frame in her pregnancy did you run it? Have you spoken with the distributor/office to see if a replacement test might be sent or if the one you used might have been old or corrupted somehow during shipping? I'm like you, when I test for a baby, I want to KNOW! lol