| ICD9CM for diagnosis codes | ICD10 | Standard ICD9 maps 1:1 to ICD10, but some ICD9CM codes do not exist in standard ICD10 |
| ICD9 for procedure codes | OPCS4 | Not an exact science—requires expert clinical coding; list of “operating room” procedures also needed |
| Diagnosis related groups, also grouped into major diagnostic categories | Healthcare Resource Groups | No mapping exists |
| Transfer from an “acute facility” | Source of admission | Requires some assumptions of what types of institution could have acute facilities |
| Transfer to an “acute facility” | Provider code | Requires linkage between admissions and a list of acute trusts |
| Elective procedure | Method of admission | This is straightforward |