Coding Knowledge and Skills · 3 min read
Primary Diagnosis and Procedure
Defining the Principal Diagnosis
The principal diagnosis is defined as the condition established after study to be chiefly responsible for occasioning the admission of the patient to the hospital for care. This definition applies specifically to inpatient coding. The phrase "after study" indicates that the principal diagnosis may not be apparent at admission and may differ from the admitting diagnosis.
Determining the principal diagnosis requires analysis of the entire record. The coder must identify which condition, after all testing and evaluation, was the primary reason the patient required inpatient hospital care. This determination directly impacts DRG assignment and reimbursement.
Principal Diagnosis Selection Guidelines
When two or more interrelated conditions, or two or more diagnoses, equally meet the definition of principal diagnosis, either may be sequenced first unless the circumstances of admission, the therapy provided, the Tabular List, or the Alphabetic Index indicate otherwise. Resource use or payment is not the deciding factor.
When the admission is for treatment of a complication, the complication code is generally sequenced as the principal diagnosis. For example, if a patient is admitted for treatment of a mechanical complication of a cardiac pacemaker, the complication code is principal even though the underlying heart condition necessitated the pacemaker.
When symptoms are followed by contrasting or comparative diagnoses, the symptom code is sequenced first, followed by the contrasting diagnoses. When a diagnosis is documented as probable, suspected, likely, questionable, possible, or still to be ruled out at discharge, the condition is coded as if confirmed for inpatient records.
The uncertain-diagnosis rule applies to inpatient admissions to short-term acute care, long-term care, and psychiatric hospitals; it does not apply to outpatient encounters.
| Situation | Principal diagnosis rule |
|---|---|
| Symptom with a related, established definitive diagnosis | Do not use the symptom code as principal; code the definitive diagnosis |
| Two or more diagnoses equally meet the definition | Either may be sequenced first unless the circumstances of admission, therapy, or the Index/Tabular indicate otherwise |
| Two or more comparative or contrasting conditions ("either/or") | Code both as if confirmed; sequence according to the circumstances of admission |
| Symptom followed by contrasting or comparative diagnoses | Sequence the symptom first; code the contrasting diagnoses as additional |
| Original treatment plan not carried out | Still sequence the condition that, after study, occasioned the admission |
| Admission for a complication of surgery or other care | The complication code is principal, with additional codes for specificity as needed |
| Uncertain diagnosis at discharge ("probable," "suspected," "likely") — inpatient | Code as if the condition existed or was established |
| Admission from outpatient surgery | Complication if admitted for one; otherwise the reason for the outpatient surgery, unless an unrelated condition caused the admission |
Outpatient Principal Diagnosis Considerations
For outpatient encounters, the first-listed diagnosis represents the reason for the encounter. Uncertain diagnoses are not coded in outpatient settings; instead, code the symptoms, signs, or findings documented. This fundamental difference between inpatient and outpatient coding must be thoroughly understood.
Principal Procedure Identification
Under UHDDS, the principal procedure is the one performed for definitive treatment rather than for diagnostic or exploratory purposes, or the one necessary to take care of a complication. When more than one procedure meets that definition, the one most related to the principal diagnosis is selected as principal.
For DRG assignment purposes, the principal procedure designation can significantly impact reimbursement. Operating room procedures generally carry greater weight than non-operating room procedures.
Sequencing Multiple Diagnoses and Procedures
After the principal diagnosis, secondary diagnoses are sequenced based on their clinical significance and resource consumption. Conditions that required clinical evaluation, therapeutic treatment, diagnostic procedures, extended length of stay, or increased nursing care should be coded and sequenced appropriately.
Procedure sequencing follows similar logic. After the principal procedure, additional procedures are sequenced based on their significance to the episode of care. All significant procedures performed during the encounter should be coded.
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