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UPDATE: More Information On ICD-10 Changes from ICD-9

Note: The CDT 2016 Companion will include a chapter with new and revised codes that correspond to ICD-10-CM codes – on sale now at

Additional information about ICD-10 is available:

Specific Changes to Diagnosis Code Reporting: ICD-10-CM

How does the ICD-10-CM diagnosis code set differ from the ICD-9-CM?

  • The code set has been expanded from five positions (first one alphanumeric, others numeric) to seven positions. The codes use alphanumeric characters in all positions, not just the first position as in ICD-9.
  • As of the latest version, there are 68,000 existing codes, as opposed to the 13,000 in ICD-9.
  • The new code set provides a significant increase in the specificity of the reporting, allowing more information to be conveyed in a code.
  • The terminology has been modernized and has been made consistent throughout the code set.
  • There are codes that are a combination of diagnoses and symptoms, so that fewer codes need to be reported to fully describe a condition.

Examples of the enhancements made to the ICD-10-CM code set:

  • It enables reporting of laterality (right vs. left designations), reflecting the importance of which side of the body or limb (e.g., left arm, left kidney, left eye) is the subject of the evaluation.
  • It restructures reporting of obstetric diagnoses. In ICD-9-CM, the patient is classified by diagnosis in relation to the episode of care. In ICD-10-CM, the patient is classified by diagnosis in relation to the patient’s trimester of pregnancy.

No Clear Mapping Between ICD-9-CM and ICD-10-CM Code Sets
One of the most important concerns in the transition from ICD-9-CM to ICD-10-CM codes is that there is no simple mapping or translation from the former to the latter. There are some one-to-one correspondences, but often there are one-to-many, many-to-one, many-to-many, or no correspondence at all. This is a major implementation consideration for the state Medicaid agencies. There are some tables and crosswalks that have been published to ameliorate this problem (such at the general equivalence tables published by the National Center for Health Statistics), but additional study will determine how coding will change.

Specific Changes to Inpatient Hospital Procedure Code Reporting: ICD-10-PCS
The ICD-10-PCS (Procedure Coding System) code set will only be used to report procedures on inpatient hospital claims. Other code sets (HCPCS, CPT-4) will continue to be used to report procedures for other types of claims. This code set was developed in the United States by the CMS. It is not yet used elsewhere, and it is not related to the ICD-10-CM code set. It is an update from the currently used ICD-9 procedure code set, and has been changed as drastically as the diagnosis codes.

Characteristics of ICD-10-PCS Codes

ICD-10-PCS inpatient hospital procedure codes have seven positions (expanded from five positions in the ICD-9-CM code set), with each position having a specific meaning. The ICD-10-PCS code set has four basic characteristics:

  • It allows for unique coding of inpatient hospital procedures so that procedures can be readily distinguished
  • It provides significant room for expansion, allowing for the code set to incorporate new procedures and devices
  • It makes use of a standardized, well-understood terminology that reflects the current practice of medicine
  • It demonstrates consistency in coding from chapter to chapter

Why Change from the ICD-9-CM Code Set to the ICD-10-CM/PCS Code Set?
The practice of medicine has changed dramatically in the last 25 years or so. There have been many new conditions discovered, many new treatments developed, and many new types of medical devices have been placed into service. The ICD-9 code set was not designed to capture all of this progress, and as such, has become bogged down with many types of modifications to attempt to capture information. The ICD-10 code set is much better at describing the current practice of medicine, and has the flexibility to adapt as medicine changes.

Diagnosis codes and procedure codes permeate almost every business process and system in both health plan and provider organizations. Diagnosis codes are key for determining coverage and are used in treatment decisions. From plan design to statistical tracking of disease, these codes are a crucial part of the way health plans — including State Medicaid agencies — run their programs.