Hi Doubt, Thanks for getting in touch with us. Yes, this is completely normal. We do state in the instructions for use and the product insert that the test should not be re-read more than an hour after the test has been conducted. The strip can change colour and in fact additional marks can develop on the strip that are nothing to do with the test or HIV. You should only read and interpret the result of your test ideally at the 15 minute mark described in the test and certainly not more than an hour after the test has been performed. I hope that this answers your question and removes the doubt. Kind regards Gary Carpenter BioSure (UK) Limited