As baseball spring training is already underway, it seems appropriate to quote a New York Yankees Hall of Famer who is widely regarded as one of the greatest catchers in baseball history. Yogi Berra once said “It’s hard to make predictions, especially about the future.”

Yogi might be known as much for his many famous quotes as he was for appearing in 21 World Series as a player, coach or manager. But his words here ring true in the world of healthcare too, as predicting the reimbursement impact from the transition to ICD-10 is a topic that understandably is a major issue for organizations. In this article we will evaluate two documented projects and research pertaining to estimating this impact.

G stands for General, as in General Equivalence Mappings (GEMs)

The Centers for Medicare & Medicaid Services (CMS) and the Centers for Disease Control and Prevention created the General Equivalence Mappings (GEMs) to ensure the existence of consistent national data when the U.S. makes the transition. While the mappings between ICD-9-CM and ICD-10-CM/PCS will play a critical role in the transition, understanding the objectives and limitations of the GEMs is invaluable to determining the potential impact to your reimbursement. The GEMs were developed as a dictionary meant to bridge the language gap between the two coding sets and to help users understand, analyze and manage the translation of one code set to the other.

As published in the AHIMA’s “Putting the ICD-10-CM/PCS GEMs into Practice,” a Journal of AHIMA article, the GEMs cannot be used:

  • “As simple crosswalks. They are reference mappings to assist users in navigating the complexity of translating meaning from the contents of one code set to the other code set according to the definitions and rules of the applicable code set.
  • By a system or application in unaltered form to get from one code in the source code set to one code in the target code set. It is up to end users, including payers, vendors, and providers, to use the GEMs as a basis for converting systems or as a basis to create applied mappings that meet their specific needs (development of applied mappings is discussed in greater detail later).

The GEMs should not be used as a substitute for learning how to use the ICD-10-CM/PCS code sets. Coding professionals should not use the GEMs as a means to code health records for external reporting or other administrative purposes, such as reimbursement or state data reporting. When coding health records, codes should be assigned using an ICD-10-CM/PCS code book or coding software and should be based on health record documentation. Mapping simply links concepts in the two code sets without consideration of context or specific patient encounter information, whereas coding involves assigning the most appropriate code based on health record documentation and applicable coding guidelines.”



CMS ICD-10 MS-DRG Conversion Project

A project CMS recently undertook was to convert the ICD-9-CM-based Medicare Severity – Diagnosis Related Groups (MS-DRGs) to ICD-10-CM and ICD-10-PCS codes.  The project was an exercise meant to evaluate the effectiveness of the General Equivalence Mappings (GEMs) and to learn how best to use them in converting data. The objective of the project was to produce an ICD-10 version of MS-DRGs that replicated the ICD-9-CM version.

The findings of the project included simulating payments by replicating ICD-10 MS-DRGs from the historical ICD-9 MS-DRGs data, and doing so identified material deficiencies in simulating reimbursement impacts following the transition to ICD-10. Key findings of the ICD-10 MS-DRG conversion project are as follows:

  • The converted ICD-10 database developed for the project was created with records coded in ICD-10, but at a level of specificity corresponding to ICD-9-CM. In other words, the records were coded in ICD-10 based only on the information available in ICD-9-CM. When additional information was required to complete the ICD-10 coding, that information was inferred by randomly selecting from alternative possibilities. Such an approach is sufficient for the purpose of comparing the impact of replicated versions of MS-DRGs; however, such an approach could not be used as the basis for establishing payment weights of optimized ICD-10 MS-DRGs.
  • Because there is no available substantial database coded in ICD-10, there is no way of recalibrating the MS-DRG payment weights to correspond to ICD-10-optimized MS-DRGs. As such, the advantages of the increased specificity of ICD-10 are lost. If the ICD-10 MS-DRGs had been optimized for ICD-10, there could have been a substantial shift of patients across MS-DRGs, creating inconsistencies with the existing MS-DRG payment weights.


Except in these very narrow circumstances, it is not possible to convert an ICD-9-CM database to ICD-10, corresponding to the full specificity of ICD-10, reliably. This is because the necessary information is simply not available in ICD-9-CM. CMS has documented that it plans to begin determining the optimization of MS-DRGs for ICD-10 once ICD-10-coded data becomes available, allowing the MS-DRG payment weights to be recalibrated simultaneously.

About the Author

John Pitsikoulis, RHIA, is a Strategic Advisory Services Client Executive and ICD-10 Practice leader at CTG Health Solutions (CTGHS). John is responsible for the strategic advisory services such as ICD-10, EMR clinical documentation integration program, and Computer Assisted Documentation Services. John has over 25 years of Health Information Management (HIM), coding, and compliance consulting experience working with clients on ICD-10 services, RAC, coding, and clinical documentation improvement engagements.

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Article citation:
AHIMA, “Putting the ICD-10-CM/PCS GEMs into Practice,” Journal of AHIMA 81, No. 3 (March 2010): p. 46-52.

Centers for Medicare & Medicaid Services (CMS), “Converting MS-DRGs 26.0 to ICD-10-CM and ICD-10-PCS.”

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