How can a runner tell a heel bone stress fracture from plantar fasciitis

I just did a consultation call with an injured runner who had a really interesting history with his heel pain. There was some concern that he might actually have a calcaneal stress fracture and not a plantar fascia issue. 
 
In case you don't know, "calcaneal stress fracture" is just the medical term for a stress fracture in the heel bone.
 
The heel bone is the largest bone in your foot, and runners can sometimes develop a stress fracture in the heel bone. 
 
They are relatively rare, but there are a couple of ways that you can get these stress fractures.
 
The good news is calcaneal stress fractures heal pretty quickly. But if you have one, you really don't want to run on it.
 
How can a runner tell a heel bone stress fracture from plantar fasciitis? 
 
Well, that's what we're talking about today on the Doc on the Run podcast.