In medical coding, the primary diagnosis is the condition that requires the most resources and care, while the principal diagnosis is the condition that causes the patient to be admitted into a hospital or other care facility. In most cases, the primary and principal diagnoses are the same, the Agency for Healthcare Research and Quality says.
The purpose of the principal diagnosis is to establish what condition is causing the symptoms that the patient experiences. In rare cases, the patient has more than one principal diagnosis, meaning that a medical condition interrelates with another condition, according to Yaki Technologies. This also occurs when more than one separate principal diagnosis is equally responsible for a hospital stay. For example, a patient who has a chronic disease might have multiple recent manifestations that result in an inpatient stay. In this case, the principal diagnoses are the manifestations that caused the most recent hospital visit.
The purpose of the primary diagnosis is to establish where doctors focus the majority of resources to treat a condition. The primary diagnosis is not always the principal diagnosis because a symptom of a principal condition can cost more money and resources to treat than the underlying condition that causes it. Coding the primary and principal diagnoses separately is a requirement for all medical facilities, even if the condition is the same for both.