Diagnosis and Procedure Coding Resources

Providers that bill Medicare use codes for patient diagnoses and codes for care, equipment, and medications provided. “Procedure” code is a catch-all term for codes used to identify what was done to or given to a patient (surgeries, durable medical equipment, medications, etc.). Understanding and identifying the codes relevant to one’s study question is a key part of analyzing claims data. Each year, codes are added, codes are discontinued, and new codes may replace previously-used codes. In order to fully identify procedures and diagnoses of interest, it is important that researchers know the codes in use during their study period.

ResDAC staff are not coding experts and 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.

A source of both diagnosis and procedure code information is a codebook. They are available for purchase or may be available at an academic or medical library. Several different publishers offer codebooks and they publish versions of various level of detail and guidance, such as Standard, Professional, and Expert. Some versions will include lists of retired codes in addition to current codes, while others may contain current codes only.

Codebooks are specific to a fiscal year; CMS’s fiscal years begin on October 1. This means, if a researcher is interested in studying 2014 calendar year claims, for example, codebooks for both 2014 and 2015 are necessary because it crosses CMS’s fiscal years.

Diagnoses

ICD diagnosis codes are present in all Medicare claim-level and stay-level files: Inpatient, Outpatient, Carrier, Skilled Nursing Facility, Hospice, Home Health, Durable Medical Equipment, and MedPAR. Starting in 2011, institutional providers are able to enter up to 25 diagnosis codes for a single claim where previously only 10 were allowed. Non-institutional providers are permitted 12 diagnosis codes where previously only 8 were allowed. The first code listed is considered the primary diagnosis code. In addition, the non-institutional claims include an ICD diagnosis code on each line item being billed.

Procedures

ICD procedure code fields are present in the institutional claim-level and stay-level files: MedPAR, Inpatient, SNF, and Outpatient. However, ICD procedure codes are not the basis for payment for all of these types of care. In general, when they are not the basis for payment, the fields will be present, but empty.

ICD-9 Diagnosis and Procedure Codes

ICD-9 (International Classification of Diseases, 9th edition) codes were used through September 30, 2015. Fiscal Year 2006-2015 ICD-9 code lists are available for download on the CMS website. This list contains less detail than a purchased version.

ICD-10 Diagnosis and Procedure Codes 

On October 1, 2015, CMS transitioned from ICD-9 to ICD-10. The claims files include fields that indicate whether the listed ICD code is ICD-9 or ICD-10. ICD-10 codes for Fiscal Year 2014 through the current fiscal year are available for download on the CMS website.

For information related to managing the transition when conducting analyses, please see the document "Managing the Transition from ICD-9 to ICD-10" in the Attachments section below.

For some types of care, procedures are billed using CPT (Current Procedural Terminology) /HCPCS (Healthcare Common Procedure Coding System) codes, rather than ICD. CPT codes, also called Level I HCPCS codes, are used to bill physician services and they are copyrighted by the American Medical Association (AMA). There are three categories of HCPCS codes. CPT/Level I HCPCS codes are five position numeric codes. Level II HCPCS codes are five position alpha-numeric codes. Level II HCPCS were developed by CMS and are primarily used for equipment, supplies, or non-physician services that are not covered by an AMA CPT code. Level III HCPCS codes existed in the past but these were local codes and have been discontinued.

Level I HCPCS (CPT) Code Resources

The CPT (Level I HCPCS) codes are copyrighted by the AMA. Complete code lists (electronic and hard copies) are for purchase only. However, the American Medical Association website includes a CPT code search tool. Researchers can search by the 5 digit CPT code or a keyword to identify codes and/or definitions.

In addition, the CMS website allows researchers to search the Physician Fee Schedule for pricing information for specific HCPCS 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 Codes

There are electronic and hard-copy Level II HCPCS codebooks for purchase.  However, Level II HCPCS codes (also called Alpha-Numeric HCPCS codes) are not proprietary and are available for download on the CMS website.

HCPCS and CPT codes are stored in the same field* and this field is present in all the claim-level files: Inpatient, Outpatient, Carrier, Skilled Nursing Facility, Hospice, Home Health, and Durable Medical Equipment. Like the ICD procedure code, HCPCS/CPT codes are not the basis of payment for all these types of care. In general, when they are not the basis for payment, the fields will be present, but empty.

*Warning: HCPCS / CPT Code Field

There are instances in which the HCPCS/CPT code field is populated, but not with a HCPCS / CPT code.  For example, in the SNF and Home Health files the HCPCS / CPT code field stores the case-mix grouping that Medicare used to pay for services.

For additional information about codes used to bill Medicare for specific types of care, please see the Medicare Claims Processing Manual. The manual lists which codes are used to bill each care type of interest. Consulting with a medical coder at your organization may be helpful as well as searching the literature through a website such as PubMed for examples of codes that others have used when studying a particular topic.