The primary diagnosis refers to the patient condition that demands the most provider resources during the patient’s stay. There is often confusion surrounding primary and principal diagnoses and, consequently, the terms are commonly used interchangeably. While these can be (and frequently are) the same diagnosis in practice, their definitions are distinct. While a principal diagnosis is the underlying cause of patient symptoms, the primary diagnosis is used for healthcare billing purposes.
Primary diagnoses play an important function in how providers are reimbursed for healthcare services. Whether it is diagnosis-related grouping (DRG) or ICD-10 coding, the primary diagnosis is used to inform the payer how much the provider is owed after a medical claim is submitted.