How accurate home pregnancy tests?

I have had a really light period over the last few days but thought i had had my period earlier a few weeks ago, so I decided to do a pregnancy test. I ended up doing 3 & they all returned a positive result. I know my hcg level must be high to get a result at night but before we get to excited I wanted to check if there is any chance that having my period could affect the result of a pregnancy test?