I Had A Full Physical By My General Practitioner Back

I had a full physical by my general practitioner back in October of 2017. My results were fine. About a month later I had an appointment with my gynecologist at which time they did a bone density exam. About a week ago I received a phone call from the gynecologist office stating that the Dr would like to have a consult with me regarding the bone density test and to please bring any blood work results from my physical. My question is ...1. What does blood tests have to do with bone density...2. And why a consult? I already know I need to take calcium and vitamin D so if I am at risk for osteoporosis couldn't they just explain that over the phone and recommend that I take vitamin D and Calcium?