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

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 with 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. WHO publishes minor updates every year and major updates every three years.

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.

According to the American Health Information Management Association, ICD-10 provides better mapping from SNOMED CT, a multilingual vocabulary of clinical terminology that is used to capture the clinical data of a care episode. SNOMED CT to ICD-10 mapping can enable computer-assisted coding that improves the accuracy, efficiency and consistency of coding. ICD-10 procedure codes can also provide specific information about how a healthcare provider approached a medical procedure and what type of medical device was used.

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; and
  • 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 with 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. The seventh character was added to further specify a diagnosis and most commonly captures data about the treatment phase, as follows:

  • A (initial encounter). Although the name implies it is the patient's initial visit, initial encounter refers to the period during which the patient is receiving active treatment for a condition.
  • D (subsequent encounter). Subsequent encounter refers to an encounter after the patient has received active treatment, during the recovery phase.
  • S (sequela). Sequela refers to a complication or condition that is a direct result of an injury, such as a scar.

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 a 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 vs. 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?

All HIPAA-covered entities were required to transition to ICD-10. While non-HIPAA-covered entities aren't required to transition, they can still adopt the coding system, which could potentially help the noncovered entities expand into more detail on injuries. 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.

Work on ICD-10 first began in 1983 and was endorsed by the 43rd World Health Assembly (WHA) in May 1990. Some countries began using ICD-10 codes in 1994, with the U.S. being one of the last developed countries to adopt the revision.

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. Physicians, in particular, opposed the new revision, with groups like the American Medical Association lamenting the cost of ICD-10 implementation, believing it would take away resources from other areas. Below is a brief timeline of the delays that slowed down ICD-10 implementation:

  • 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. Then-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.

ICD-10 vs. ICD-11

WHO released an advance preview of ICD-11 on June 18, 2018, with 55,000 codes for causes of death, diseases and injuries. The new revision was designed to simplify the coding structure, so healthcare providers can more easily record medical conditions.

This edition is also the first to be completely electronic, so it can integrate with electronic data sources and is free to download online for personal use. Experts can contribute to the revision process through the ICD-11 online platform, which will allow them to make comments and proposals for ICD categories and definitions.  

ICD-11 adds gaming disorder to the addictive disorders section and expands sections on allergies and immune system disorders, cancer, cardiology, dementia, diabetes and infectious diseases. The new revision will also include new chapters on sexual health and traditional medicine.

ICD-11 will be presented at the WHA in May 2019 for adoption by countries and other parties, and it will go into effect on Jan. 1, 2022, if the WHA endorses it. However, adoptees are encouraged to begin planning their transition to ICD-11 now, which may include translating it into their language.

This was last updated in September 2018

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