Crinone Progesterone Gel

So I heard back from the doctor office and my progesterone was 4.8 but there is no way of telling because the Crinone is not detectable in blood. Im really confused here. So the pharmacutiucal company is selling a drug that claims to raise your progesterone but there is no way to tell if its working? I am really just beyond frustrated today. I am so ready for IVF and I honestly think that IUI is a waste of time and money.