10mIU is the most sensitive - it can pick up hCG at half the concentration as the other (milli international units, if you wondered what mIU stood for).

Best of luck for your test Jenny!

Oh, I forget to say before that I always recommend waiting for as long as possible as I hate to see a BFN, it's worse than a period for me. That's why I was 8w gone before I found out about my baby, I couldn't put of testing any longer in case there was a problem with me! Other people prefer to know as early as possible, so good for you for not wanting to wait!