Question!!! And it's a doozy so please read!!! It's about tests, lines and HCG!

Ok so most pregnancy tests detect HCG at 25miu. So my question is... if you get a super faint line on one, is this 25miu? I realize this may sound dumb... but if your HCG is higher you typically get a darker line. So if your HCG is lower than 25miu does it still pick up with a faint line even though the test detects 25miu? Lol I'm all in my thoughts right now.