Which coding system is used for diagnosis coding and reporting on claims regardless of the provider?

• A. CPT
• B. HCPCS
• C. CDT
• D. ICD-9

Answer: (D)

Diagnoses on claims are described using a universal diagnosis coding system that standardizedly represents a patient’s conditions. ICD-9-CM is the diagnosis coding system used to convey those conditions on claims, regardless of which provider submits the bill.

CPT codes are reserved for reporting procedures and services performed, not the diagnoses themselves. HCPCS covers products, supplies, and certain services that may fall outside CPT’s scope. CDT is specific to dental procedures. So while CPT, HCPCS, and CDT serve important coding roles, they do not function as the universal diagnosis coding on claims—that role belongs to ICD-9-CM (with ICD-10-CM/ICD-10-PCS used in many settings today).