Atheist – does not believe (in God).
Agnostic – does not have knowledge (about God)
Applying these concepts in the practice of medicine, a physician is agnostic if he does not have knowledge on a certain medical condition. He is an atheist if he does not believe the management of a medical condition should be done based on published evidence-based clinical practice guidelines. This is the strictest application of the concept of atheist and agnostic in the practice of medicine.
However, should all published evidence-based clinical practice guidelines be considered foolproof? gospel-truth? NO. They will change overtimes. They will change depending on the circumstances. This is the argument against atheist in the practice of medicine.