Fee-for-service payment hinges on billing discrete services with CPT codes, using ICD-10 codes to justify why the service was needed. Hospital Ancillary Services fall into this pattern because these are the facility-based, individual services (like imaging, labs, therapies) billed separately with CPT codes, each tied to a supporting ICD-10 diagnosis. Clinicians’ Professional Services are the physician or clinician’s own billable work (evaluations, procedures) also billed by CPT codes and justified by ICD-10 diagnoses. This combination captures the classic per-service, CPT-driven reimbursement from both sides: the facility side and the professional services side. Inpatient room charges and pharmaceutical supplies aren’t billed as separate CPT-based services; they’re typically bundled into broader payment streams (like DRGs or facility charges). Home health and durable medical equipment are reimbursed under different systems and code sets (HCPCS for DME, PPS for home health), not the same CPT-based fee-for-service model.