TTC w/ a miscarriage question about...

Confirming miscarriage with the doctors:

If I think I had a miscarriage at 4 weeks pregnant, would blood work still be able to detect HCG 48 hours later? I’ve been told it should be able to, but I know I’m so early it might not. I’m just asking so that way I can be confident and sure with my results and not second-guess them and drive myself crazy.