Understanding the appropriate procedure and diagnosis codes for a particular study question is an important part of analyzing Medicare data. These codes are very specific and can change from year to year as new codes are added and others are discontinued. It is very important that researchers identify the correct codes for their study. The CMS datasets will contain ICD-9 diagnosis codes and a mix of either ICD-9 procedure codes or Healthcare Common Procedure Coding System (HCPCS) / Current Procedural Terminology (CPT) codes depending on the file. We are not coding experts at ResDAC, so we are not able to provide specific guidance on the best codes for a particular procedure or condition. Researchers will need to use resources such as those listed below to identify and define codes of interest.
The best source of both diagnosis code and procedure code information is a codebook. They are available for purchase or may be available at an academic or medical library. Codebooks are specific to a given year and provide the most detailed information about the diagnosis or procedure code. Several different publishers offer codebooks.
While codebooks are typically our best recommendation for identifying codes of interest, there are a few other resources that researchers could try when looking for coding information. Below is a list of other possible resources broken up by type of code.
ICD-9 Diagnosis Codes
The diagnosis codes included in the CMS datasets are ICD-9. CMS has not yet transitioned to ICD-10 diagnosis codes. For more information about that future transition, please see the ICD-10 section of the CMS website.
The ICD-9 section of the CMS website provides downloadable files of ICD-9 diagnosis codes that include the full and abbreviated diagnosis title. The downloads are organized by year with updates effective each October.
ICD-9 Procedure Codes
ICD-9 procedure codes will be found in the MedPAR, inpatient, and SNF claims files. It is possible to see ICD-9 procedure codes in the hospice files, but in general, the hospice file contains very few procedure codes. See below for information about the other type of procedure code (HCPCS/CPT) that will be found in the other files.
HCPCS/CPT codes will be found in the home health, outpatient, carrier, and durable medical equipment claims files. These codes will also be found in the non-identifiable summary files such as the Part B National Summary Data File. There are three levels of HCPCS codes. Level I HCPCS codes are five position numeric codes. Level I HCPCS codes are the same as CPT codes and they are copyrighted by the American Medical Association (AMA). Level II HCPCS codes are five position alpha-numeric codes. Level II HCPCS are developed by CMS and are primarily used for items, supplies, or non-physician services that are not covered by an AMA CPT code. CMS also previously developed Level 3 HCPCS codes, but these codes have been discontinued.
Level I HCPCS (CPT) Codes
American Medical Association
The American Medical Association has developed the AMA Coding Online website that includes a CPT code search tool. Researchers can search by the 5 digit CPT code or a keyword to identify codes and/or definitions.
Medicare Physician Fee Schedule
The CMS website allows researchers to search the physician fee schedule for pricing information for specific CPT codes. The website is designed to provide pricing information and not detailed code definitions, so the code descriptions are brief.
Researchers can also download the source files for the physician fee schedule to obtain a list of HCPCS/CPT codes (all levels). Again, the descriptions are very brief and may not be specific enough for researchers needs. The files listed as “PFS Relative Value Files” will contain code descriptions.
Level II HCPCS (CPT) Codes
The CMS website provides downloadable files that contain Level II HCPCS procedure codes that include both the long and short descriptions.
If you need additional information, we also recommend consulting with a medical coder at your organization, if applicable. It may also be useful to search the literature through a website such as PubMed for examples of codes that others have used when studying a particular topic.