Hi Lily There are a number of reasons why lateral flow test results are unstable overtime. The vast majority of tests will remain in the same result state for a very long time after testing. However, some can change. The majority of the instability is caused by the migration of the pigment from red blood cells that can colour the test line. This would not be a late developing positive result it's just colour from the sample discolouring the test line. I hope that this helps. Kind regards Gary

Thank you Gary for responding. One last question, you wrote 'reading the result more than an hour after taking the test is not recommended', would you be able to tell me why that is??

Done a 9 week test that came back negative and a 12 week test same result what's the odds this could be wrong and I'm passive worried to death

Hi Lily There is approximately 3 times as much buffer in the test than is required for the test to run correctly. The fact that some is left over is completely normal. The amount of buffer absorbed by the test has no effect on the result. Not applying enough would mean that the test would not run and would produce an invalid result. As you have a negative result this means that sufficient blood and buffer has been applied to the test. You should take the result as you initially read the test. Reading the result more than an hour after taking the test is not recommended. I hope that this answers your questions. Kind regards Gary Carpenter BioSure (UK) Limited