I've just had a look at the pregnancy test sensitivity list, which is a sticky thread at the top of this section. It says boots are 50 mIu, tesco own is 25mIu and first response early results are 12.5mIu. The higher the number the lower the sensitivity. You would need more pregnancy hormone in your urine for the boots to pick than the tesco or frer. Does this make sense? I'm not very good at explaining things but have a look at the list and see x