SEER-Medicare: Identification of Diagnosis & Procedure Codes
One of the challenges of working with claims data is insuring that all of the relevant diagnostic and procedure codes have been included. Before finalizing a list of codes to be included in an analysis, it may be worthwhile for a researcher to print a frequency of the diagnostic/procedure codes that appear in the data. This will aide the investigator in identifying diagnoses and procedures coded in practice, as these do not always correspond to the list of codes identified by only reviewing coding manuals. This is a particularly important issue in using Medicare claims because bills sometimes contain codes unique to the Centers for Medicare & Medicaid Services (CMS). Including only ICD-9, ICD-10, and CPT-4 codes may result in services being missed and potentially erroneous findings. In addition, diagnosis and procedure codes change over time. Longitudinal studies should include the codes that were are relevant for all years of data.
For studies using Part B claims, services and procedures are coded using HCPCS (Healthcare Common Procedure Classification System). HCPCS codes have three types: Level I HCPCS are composed of the CPT-4 codes maintained by the American Medical Association; Level II and Level III HCPCS are codes used only by CMS. These codes always begin with a letter. Definitions of Level II HCPCS can be downloaded from the CMS Web site and searched by keywords. Researchers are encouraged to review the Level II HCPCS to insure that all relevant codes have been included in their analysis. Level III HCPCS, known as "local codes", are codes used in a specific locality and begin with W, X, Y, or Z. Documentation of definitions of local codes is sparse and these procedures cannot be defined.
Chemotherapy, radiation therapy, and screening procedure codes frequently included in SEER-Medicare analyses are available.