Precisely what are employers looking at when they take blood as a part of a new hire physical?

They just want to make sure you are healthy and can do what the job duties that will be required of you. If you' re going to be in a work environment where you will have close physical contact with other employees or customers they want to make sure you do not have a contagious disease that will put others who come in contact with you at risk of contamination.

They want to make sure you are not into heavy drugs or alcohol - factors that put them at risk for theft, etc.

There are many other reasons and I do not have the time or space to describe all of them - but basically when you work for a company - your are representing their professionalism to both the clients and the trade.

Drugs & alcohol

That would be drugs! Good luck