HCPCS Level II codes are alphanumeric medical diagnostic codes, primarily for non-physician services such as ambulance services and prosthetic devices,. They represent items, supplies and non-physician services not covered by CPT-4 codes (Level I). Level II codes are composed of a single letter in the range A to V, followed by 4 digits. Level II codes are maintained by the US Centers for Medicare and Medicaid Services (CMS). There is some overlap between HCPCS codes and National Drug Code (NDC) codes, with a subset of NDC codes also in HCPCS, and vice-versa. The CMS maintains a crosswalk from NDC to HCPCS in the form of an Excel file. The crosswalk is updated quarterly.