Outpatient primary diagnosis is the reason or the symptom that brings the patient to seek medical attention. The more appropriate term for this is “First listed diagnosis”. For example if a patient has chest pains and goes to the ER, the primary diagnosis would be chest pain until tests are ran and an actual diagnosis is made. Which brings us to inpatient principal diagnosis. The principal diagnosis is once the patient has been thoroughly evaluated and a diagnosis is made. Another example is once the patient gets to the ER and says they are having chest pains and tests are run, let’s say an EKG. The physician makes a diagnosis that the patient is having a heart attack. This would be the principal diagnosis and the reason the patient is being