What is the most important definition a coder should know?

Answer;

-Principal diagnosis

Explanation;

-Principal diagnosis is a condition established after study that is chiefly responsible for the admission of the patient to the hospital. The principal diagnosis is defined as the condition, after study, which occasioned the admission to the hospital.

-The principal diagnosis is not necessarily what brought the patient to the ER, but rather, what occasioned the admission. For example, a patient might present to the ER because he is dehydrated and is admitted for gastroenteritis.