Without more info, there's no way to tell for sure what it is and what it is for.
If it comes straight out of the floor, I doubt it is useful for a drain, but it's possible. Is it in an area where the builder might have planned an optional bathroom? 4.5" OD implies a 4" ID, which is a common toilet drain size. If it is a drain, you'd need to add a riser and a trap, and ideally, a vent, but you might get by with an AAV if they're allowed where you live.
Radon mitigation prep is a good possibility. Since not all homes end up needing it, they may just include the collection piping under the slab, then, after closing things in, either cap it if it's not needed, or complete the system if it is. If it is that, then, no, you can't use it as a drain as it would then just be draining into the ground underneath the house.