Inpatient Coding Guidelines, Compliance, and Regulatory Requirements
The hierarchy of authority
Inpatient diagnosis coding is governed by the ICD-10-CM Official Guidelines for Coding and Reporting (Section I conventions and chapter-specific rules, Section II principal diagnosis, Section III additional diagnoses), the UHDDS definitions, and AHA Coding Clinic advice. When sources conflict, the Official Guidelines outrank Coding Clinic, which outranks encoder prompts and habit.
UHDDS definitions to memorize
Principal diagnosis: the condition established after study to be chiefly responsible for occasioning the admission. It is not the admitting diagnosis, not the sickest condition, and not the most expensive one. Other diagnoses: conditions that coexist at admission and affect care by requiring evaluation, treatment, diagnostic workup, extended length of stay, or increased nursing care. Principal procedure: the procedure most closely related to the principal diagnosis, performed for definitive treatment rather than diagnostic purposes.
Compliance realities
Code from the entire record - discharge summary, H&P, operative and pathology reports, progress notes - never the face sheet. Diagnoses must be physician-documented; inferring a diagnosis from labs or medications is a compliance violation. Ambiguity is resolved through a non-leading physician query. Present on admission (POA) status must be captured for every secondary diagnosis because CC/MCC payment and HAC status depend on it. Know the auditors: MAC reviews, RAC, OIG Work Plan targets, DRG validation, the False Claims Act and the 60-day overpayment rule. The two-midnight rule governs Medicare inpatient admission status.
Rule of thumb
If it was not documented, it was not done; if it was documented ambiguously, query - never assign a diagnosis you inferred from clinical clues.