General Equivalence Mappings

In healthcare, diagnosis and procedure codes and their attached descriptions are the currency for many critical data transactions. Healthcare organizations rely heavily on coded data to govern reimbursement, monitor the health of the population, track trends in disease and treatment, and optimize the delivery of healthcare in the US.

The possible implementation of the ICD-10 code set is a historic opportunity to upgrade the quality of healthcare data, but like everything worth having, it comes at a cost. One cost is mapping between the old and new code sets.

A recurring theme in the ongoing ICD-10 implementation debate has been the need for a crosswalk between the old and new code sets to help the industry make the transition. The lack of an “official” mapping between ICD-9-CM and ICD-10-CM/-PCS has long been seen as a major challenge to ICD-10 implementation. The General Equivalence Mappings (GEMs) are an attempt to meet that challenge.

What Are GEMs?

The GEMs are the product of a coordinated effort spanning several years and involving the National Center for Health Statistics (NCHS), the Centers for Medicare and Medicaid Services (CMS), AHIMA, the American Hospital Association, and 3M Health Information Systems. The GEM files are a public domain reference mapping designed to give all sectors of the healthcare industry that use coded data a tool to convert and test systems, link data in long-term clinical studies, develop application-specific mappings, and analyze data collected during the transition period and beyond.

It would be impossible to produce a “one size fits all” set of mappings because a mapping is heavily dependent on its purpose. A map for reimbursement uses different rules and contains different entries than a map for research.

The GEMs are more than simple crosswalks. They cannot be used in a legacy system in unaltered form to get from a code in one set to a code in the other. A clear one-to-one correspondence between an I-9 or I-10 code is the exception rather than the rule.

It is useful to think of GEMs as two-way translation dictionaries for diagnosis and procedure codes from which crosswalks can be made for specific purposes. They elucidate the differences between the code sets and assist users in making informed decisions about how to link the codes in a way that meets their needs.

While ICD-9-CM diagnosis codes and ICD-9-CM procedure codes are maintained by two different government entities, the GEMs were developed separately but collaboratively to maintain consistency insofar as possible. The resulting files can be merged seamlessly as needed—subsets extracted, analyzed, and applied—without taking extra steps to make them compatible.

ICD-10 Codes

The International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10), of 1992, is a medical classification list by the World Health Organization (WHO), for the coding of diseases, signs and symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or diseases. The code set allows more than 14,400 different codes and permits the tracking of many new diagnoses. Using optional subclassifications, the codes can be expanded to over 16,000 codes. Using codes that are meant to be reported in a separate data field, the level of detail that is reported by ICD can be further increased, using a simplified multiaxial approach.

The WHO provides detailed information about ICD online, and makes available a set of materials online, such as an ICD-10 online browser, ICD-10 Training, ICD-10 online training, ICD-10 online training support, and study guide materials for download.

The International version of ICD should not be confused with national Clinical Modifications of ICD that include frequently much more detail, and sometimes have separate sections for procedures. For instance, the US ICD-10 CM has some 68,000 codes. The US also has ICD-10 PCS a procedure code system not used by other countries that contains 76,000 codes.

Work on ICD-10 began in 1983 and was completed in 1992.

Some 25 countries use ICD-10 for reimbursement and resource allocation in their health system. A few of them made modifications to ICD to better accommodate this use of ICD-10. The article below makes reference to some of these modifications. The unchanged international version of ICD-10 is used in about 110 countries ICD-10 for cause of death reporting and statistics.

The United States will begin official use of ICD-10 on October 1, 2014, using Clinical Modification ICD-10-CM for diagnosis coding and Procedure Coding System ICD-10-PCS for inpatient hospital procedure coding. All HIPAA "covered entities" must make the change; a pre-requisite to ICD-10 is the adoption of EDI Version 5010 by January 1, 2012. Enforcement of 5010 transition by CMS, however, was postponed by CMS until March 31, 2012, with the federal agency citing numerous factors, including slow software upgrades. The implementation of ICD-10 has already been delayed. In January 2009, the date was pushed back by two years, to October 1, 2013 rather than a prior proposal of October 1, 2011