Which option correctly describes the coding systems used for diagnoses, procedures, and inpatient procedures in the U.S.?

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Understanding how medical coding systems map to different parts of care helps explain why this combination is correct. Diagnoses are coded with ICD-10-CM across settings. Procedures and services in outpatient or professional practice are coded with CPT, with HCPCS Level II codes covering supplies and additional items not in CPT. In contrast, inpatient hospital procedures are coded with ICD-10-PCS, a separate system designed specifically for the hospital inpatient setting. So using ICD-10-CM for diagnoses, CPT/HCPCS for procedures and supplies, and ICD-10-PCS for inpatient procedures aligns with how coding is actually applied in the U.S. For example, a patient admitted with pneumonia gets an ICD-10-CM diagnosis code; a knee replacement done in an outpatient setting would be coded with CPT (and potentially HCPCS for related supplies); an inpatient surgery like an appendectomy would be coded with ICD-10-PCS.