What is the standard of care of an expert in the field of medicine?

However, courts must be particular about the expert evidence they accept in accessing the standard of care. Generally, medical specialists are not properly situated to opine on the standard of care of specialists in other areas. In addition, to the extent that an expert testifies as to what he himself would do in a situation, rather than what the standard of care requires, his testimony does not establish the standard of care nor demonstrate that the defendant doctor breached a standard of care: Bafaro v. Dowd, at paras. 32, 33 and 36. The Principles of Diagnosis

The duty to diagnose is a component of the standard of care. Mr. Justice Power described this duty in Crawford v. Penny, at para. 230(b): The duty to diagnose requires doctors to take a full history, use appropriate tests and consult or refer if necessary. They must take reasonable care to detect signs and symptoms and formulate a diagnosis using good judgment. They cannot act only on what they are told, nor ignore what they are told. Sophisticated tests and continuing knowledge of disease must be employed when appropriate.