H&H Question

This is probably a stupid question, but I am a new nurse, so here it goes anyway.........

I am working in the ortho unit (for 2 weeks now), and we have an order from one Dr that if H&H is falling to order a SOB (Stool for Occult Blood). Now I know that decreasing H&H could mean hemorrage from ortho surgery, and when they get below 10 & 30 we notify the Dr and he usually orders a couple units of blood. But what I am trying to understand is why the SOB? I thought Stool for Occult Blood would be a GI problem, not hip or knee surgery.

Thanks for any clarifications!