ICD-10-CM Diagnosis Coding for the Inpatient Hospital Setting
Conventions that drive the answer
Always search the Index, then verify in the Tabular List - the Tabular List controls. Excludes1 means 'not coded here' (the two codes cannot coexist); Excludes2 means 'not included here' (both may be coded when documented independently). 'Code first' identifies the underlying etiology that must be sequenced first; 'use additional code' means the second code is mandatory; 'in diseases classified elsewhere' codes are always secondary. Combination codes capture etiology plus manifestation in a single code. The placeholder X preserves the seventh-character position.
Inpatient-specific rules that trip candidates
Uncertain diagnoses: for inpatient admissions a condition documented as probable, suspected, likely, or 'rule out' is coded as if it exists - the opposite of outpatient rules. Chronic conditions treated during the stay are coded; 'history of' Z codes are used only when the condition no longer exists. Status Z codes (Z79, Z95, Z96) can occasionally be principal. Sequelae codes require the late effect code first followed by the residual condition.
High-yield clinical clusters
Sepsis: code the systemic infection (A41.-) first, then the localized infection; severe sepsis requires documented organ dysfunction with R65.21. Diabetes with hypoglycemia, CKD, or a skin ulcer requires a combination code. Acute on chronic heart failure has its own code (I50.23 systolic, I50.33 diastolic). Pneumonia is coded by organism; 'walking pneumonia' does not default to a specific organism.
Worked example
Documentation reads 'AKI with ATN, resolved.' ATN (N17.0) already means acute kidney failure with tubular necrosis, so N17.9 is not added. If the record only says 'acute renal failure,' N17.9 is correct.