Hospital Urine Test accuracy?


I sprained my ankle the other night and had to get an X-ray at the hospital. I told the nurse there is a chance I am pregnant but I don't know yet (would have been ovulating around 4-7 days ago). He said that they can detect it pretty early and did a urine sample.

It came back negative but I can't stop thinking about how accurate it actually could be? Is there some sort of special test they do there that I haven't heard about? I thought HCG levels would be far too low to detect at that point? I am starting to get my hopes up again because I feel like there is no way they could actually tell that early without a blood test .