ICD-10 (International Classification of Diseases, Tenth Revision)

Contributor(s): Scott Wallask and Kristen Lee
This definition is part of our Essential Guide: Guide to healthcare compliance resources and agencies

The International Classification of Diseases, Tenth Edition (ICD-10) is a clinical cataloging system that went into effect for the U.S. healthcare industry on Oct. 1, 2015, after a series of lengthy delays. Accounting for modern advances in clinical treatment and medical devices, ICD-10 codes offer many more classification options compared to those found in its predecessor, ICD-9.

The World Health Organization (WHO) owns, develops and publishes ICD codes, and national governments and other regulating bodies adopt the system.

ICD-10 purpose and uses

Within the healthcare industry, providers, coders, IT professionals, insurance carriers, government agencies and others use ICD codes to properly note diseases on health records, to track epidemiological trends and to assist in medical reimbursement decisions.

Why is ICD-10 important?

ICD-10 codes provide more detailed information for measuring healthcare service quality, safety and efficacy. Because better data will be provided via the ICD-10 code set, it has the potential to improve the following:

  • Value-based reimbursement
  • Outcome measurements
  • Clinical, financial and administrative performance measurement
  • The design of payment systems and claims processing
  • Reporting on new medical technology
  • Improving reimbursement systems
  • Care and disease process management

The adoption of the ICD-10 code set also allows for more accurate payment for new procedures, fewer rejected claims, fewer fraudulent claims, a better understanding of new procedures and improved disease management.

Key differences between ICD-9 and ICD-10

(Check out our video introduction to ICD-10 below.)

The list of ICD-10 codes greatly expands classification options.

For example, ICD-10-CM has 68,000 codes, compared to 13,000 in ICD-9-CM, according to the Centers for Medicare & Medicaid Services (CMS).

ICD-10 codes also have alphanumeric categories, while ICD-9 has numeric categories, and ICD-9's codes are based on three to five letters and numbers, while ICD-10's are based on three to seven letters and numbers.

Furthermore, with ICD-10, some titles have been renamed, chapters changed and certain conditions grouped together.

ICD-10 codes also provide more detail about the patient's condition. For example, if a patient broke their wrist, ICD-9 did not specify whether it was the left or right wrist, while ICD-10 offers either option. ICD-10 also presents additional details on when a patient is seen by a caregiver, and how an injury or disease is progressing or healing.

ICD-10-CM versus ICD-10-PCS

In the U.S., ICD-10 is split into two systems: ICD-10-CM (Clinical Modification), for diagnostic coding, and ICD-10-PCS (Procedure Coding System), for inpatient hospital procedure coding. These U.S.-specific adaptations conform to WHO's ICD-10 layout, while allowing for additional details found in U.S. healthcare. The U.S. took a similar approach with ICD-9-CM and ICD-9-PCS.

Another difference is the number of codes: ICD-10-CM has 68,000 codes, while ICD-10-PCS has 87,000 codes.

How are non-HIPAA and public health entities affected?

While non-HIPAA-covered entities aren't required to transition over to ICD-10, they can still adopt the coding system, which could potentially help the non-covered entities expand into more detail on injuries, for example. This added detail could then help organizations like automobile insurers and workers' compensation programs with injury classification and the coordination of benefits.

The history of ICD-10 codes

The U.S. used ICD-9 from 1979 to 2015. In those 35-plus years, supporters of ICD-10 said its predecessor had become obsolete, didn't account for modern healthcare practices and lacked ICD-10's specificity for clinical diagnoses and medical device coding.

Ironically, ICD-10 itself is 25 years old, having first been adopted by WHO in 1990. Some countries began using ICD-10 codes in 1994.

Meanwhile, ICD-11 is under development now, and WHO will release the update in 2017.

The transition to ICD-10

The ICD-10 conversion in the U.S. was delayed by lobbying, politics and general opposition to the increased amount of codes in the newer set. The following is a brief history of those delays.

Jan. 16, 2009 -- The U.S. Department of Health and Human Services (HHS) published a final rule establishing ICD-10 as the new national coding standard, with an adoption date of Oct. 1, 2013.

Aug. 24, 2012 -- HHS announced a delay in ICD-10 adoption from Oct. 1, 2013, until Oct. 1, 2014, to allow healthcare systems more time to prepare for the transition.

March 2013 -- At the 2013 HIMSS (Healthcare Information and Management Systems Society) meeting, a CMS administrator said ICD-10 would not be delayed past Oct. 1, 2014.

April 1, 2014 -- President Barack Obama signed a Medicare reimbursement bill from Congress that included a delay in ICD-10 implementation from Oct. 1, 2014, until Oct. 1, 2015.

This was last updated in April 2017

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How have you prepared for ICD-10 implementation?
How has the implementation of ICD-10 helped your organization better classify illnesses?
I was taught in ICD-9-CM coding my latest certificate was earned in July 25, 2006. As I was doing my continuing education in nursing LPN for my licensure in the state of New Jersey, I started updating my self in reading on the conversion. I read the ACA in my continuing education. It stated that coding was going to be one of the most jobs in demand. Also, the change from ICD-9-CM to ICD-10-CM. In addition I updated myself through Advance as well. I read many articles on the conversion to ICD 10. I am a 25 1/2 year LPN. I started pursuing the HIT Career. I am currently enrolled in a Medical Billing and Coding Certificate Program. I am familiar with what areas in coding the CMS has a high interest. I am doing the ICD-10 class currently. Things do not stay the same. I look forward to completing the class. Claudette Singleton LPN.


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