The International Statistical Classification of Diseases (ICD) is a set of codes from the Unified Medical Language System (UMLS). ICD is used to classify diseases, symptoms, and other health problems.
The International Statistical Classification of Diseases (ICD) is published by the World Health Organization (WHO). ICD-9 has been used in the United States since 1977 for reporting statistics and billing to Medicare, Medicaid, and insurance companies.(1) The code set was developed before computers were widely used to process medical data aside from billing, indexing, and statistics. The World Health Organization has since published a revised set of codes called ICD-10 in 1992. The new scheme allows for 155,000 unique codes as opposed to the 17,000 of ICD-9-CM.
History and Background
The first coding system was developed in 1893 in France by a physician, Jacques Bertillon. The system was called International List of Causes of Death (ILCD) or the Bertillon Classification of Causes of Death at that time. Its primary purpose was to compile mortality statistics . The WHO became custodian of ICD in 1948 and adopted the ILCD, which was expanded to include morbidity coding. Hence, with the Sixth Revision in 1948, the ILCD evolved as means to code diseases for more than just cause of death. From then onwards, it was called the International Statistical Classification of Diseases, Injuries, and Causes of Death (ICD) .
ICD-10 allows for greater granularity and specificity of reporting data. In addition, the system solves many of the problems of ICD-9, most notably the problem of expandability. Previously, newly classified diseases and procedures were simply added to the end of the current list of codes. In 1998, the National Center for Health Statistics released a modification of ICD-10 for the reporting of morbidity data and thus began the process of converting U.S. government departments to the new code set.(2) In 2008, CMS announced that all diagnosis data for claims processing would have to use ICD-10 beginning in October 2011.
The proposed implementation is being met with resistance by U.S. providers and insurers due to the cost of implementation and increased administrative complexity. One estimate puts the cost at $285,000 for a 10-physician practice over the 3-year implementation period between 2008 and 2011.(3) Although HHS's goal is to reduce improper or inaccurate charges, the transition is expected to result in two-to-threefold increases in rejected claims in the short-term. Some believe the timeframe for the changeover is unworkable, although the legislation by Congress in 2006 proposed the change be completed by 2009.(4)
As medical science has progressed and new diseases have been identified, named and described, the code lists have been updated. The rationale for the periodic revisions has been to reflect advances in medical science and changes in diagnostic terminology. The upgrade in 1977 to ICD-9 was the first time procedure codes were added. In 1977, the clinical modification of ICD-9 was developed by NCHS and ICD-9-CM was adopted for use in US in 1979. Since then, ICD-9-CM classification is being used in assigning codes to diagnoses associated with an inpatient, outpatient, and physician office utilization in the United States.  In 1992, the next revision of the codes was completed by WHO and ICD-10 was released. The code set allows more than 155,000 different codes and permits tracking of many new diagnoses and procedures. The world adopted ICD-10 quickly. Some countries have even created their own versions of ICD-10, for example, Canada introduced ICD-10-CA in 2000. Despite it being almost 20 years since the introduction of ICD-10, many countries have still not adopted it for mortality and morbidity coding, US being one of them.
On January 16, 2009, HHS published a regulation requiring the replacement of ICD-9 with ICD-10 as of October 1, 2013 . Thus, the United States will begin its official use of ICD-10 on October 1, 2013, utilizing clinical modification of ICD-10 (ICD-10-CM) for diagnoses coding and the procedure coding system (ICD-10-PCS) for inpatient procedure coding . All HIPAA “covered entities” must make the change; a prerequisite to ICD-10 is the adoption of electronic billing (EDI) version 5010 by January 1, 2012 .
According to a November 17th, 2011 press release by Centers for Medicare and Medicaid Services (CMS), enforcement of the verison 5010 HIPAA transaction standards will be delayed until March 31, 2012.
|ILCD Revision 1||1900|
|ILCD Revision 2||1910|
|ILCD Revision 3||1920|
|ILCD Revision 4||1929|
|ILCD Revision 5||1938|
|ICD Revision 6||1949|
|ICD Revision 7||1955|
|ICD Revision 8||1965|
|ICD Revision 9||1976|
|ICD Revision 10||1989|
|ICD Revision 11 (in preparation)||2015|
Table - 1: List of International Classification of Diseases and Years of Adoption 
- Manchikanti L, Falco F, Hirsch J. Necessity and implications of ICD-10: facts and fallacies. Pain Physician. 2011; 14:E405-E425.
- Jetté N, et al. The development, evolution, and modifications of ICD10: Challenges to the international comparability of morbidity data. Med Care 2010; 48:1105-1110.
- CMS: Centers for Medicare & Medicaid Services [Internet]. Baltimore: Department of Health and Human Services; c2011. ICD-10: Providers resources; 2011 June 09 [cited 2011 Nov 16]. Available from: https://www.cms.gov/ICD10/05a_ProviderResources.asp
- CMS: Centers for Medicare & Medicaid Services [Internet]. Baltimore: Department of Health and Human Services; c2011.CMS statement: Centers for Medicare & Medicaid Services’ Office of E-Health Standards and Services Announces 90-Day Period of Enforcement Discretion for Compliance with New HIPAA Transaction Standards; 2011 Nov 17 [cited 2011 Nov 21]. Available from: http://www.cms.gov/ICD10/Downloads/CMSStatement5010EnforcementDiscretion111711.pdf
Submitted by Faiza Khan (November 2011)
- AAFP Challenges Wisdom of Adopting ICD-10. American Academy of Family Physicians. 
- Latour, Kathleen M and Eichenwald-Maki, Shirley, eds. Health Information Management: Concepts Principles, and Practice. 2nd Edition. Chicago: AHIMA, 2006.
- Switch to ICD-10 codes could be costly: HHS proposal calls for ICD-10 implementation by 2011. Renal Business Today. 
- Rushing ICD-10 Implementation Would Likely Cause Improper and Fraudulent Medicare Payments To Soar, New Report Finds. BlueCross BlueShield Association. 
February 2009 Update
Presently ICD-9-CM is used within the United States to code inpatient diagnoses and procedures as well as outpatient diagnoses. This is the U.S. clinical modification of standard ICD-9 from the WHO (World Health Organization). It contains volumes 1 and 2 for diagnosis codes and volume 3 for procedure codes and is commonly used for reimbursement and reporting purposes. Volume 3 is specifically part of the clinical modification of ICD-9 and is not part of the WHO standard. (3)
The final rule for healthcare facilities to convert from ICD-9-CM to ICD-10-CM and ICD-10-PCS was published in the Federal Register on Friday, January 16, 2009. The effective date of the final rule is March 17, 2009. The rule will update the HIPAA code sets regulation that specifies the use of ICD-9-CM. (1)
Volumes 1 and 2 of ICD-9-CM will be replaced with ICD-10-CM and volume 3 will be replaced with ICD-10-PCS. ICD-10-CM is the United States clinical modification of the ICD-10 WHO standard. ICD-10-PCS was designed specifically in the United States for inpatient procedural coding. (1) As specified in the Federal Register, ICD-10-CM and ICD-10-PCS will be used for reimbursement coding of all inpatient discharges and outpatient encounters on or after October 1, 2013.(2)
Presently Health and Human Services (HHS) estimates the cost of the change to be approximately $1,878.68 million with an estimated benefit of $4,539.63 million over 15 years. HHS has estimated that inpatient coders will require 50 hours of training and outpatient coders will require 10 hours of training.(2)
The Systematized Nomenclature Of Medicine (SNOMED) is presently being considered for use to incorporate medical concepts within an electronic health record (EHR). SNOMED is too granular for use with reimbursement and possibly with much reporting that is being done. By mapping ICD-10-CM and ICD-10-PCS to SNOMED concepts, we can develop systems that will be able to automate some processes currently being done manually for coding and reimbursement. These two terminologies can work together to provide information needed for the electronic health record.(3) SNOMED can be considered the "front end" terminology and ICD-10 can be the "back end" terminology.
Submitted by Bonnie Altus (February 2009 section)
ICD-10 Impact Statement
The upcoming ICD-10 transition scheduled for October 1, 2013 will require all HIPAA covered businesses operating in the Healthcare Industry to convert or map current systems using ICD-9 codes over to the new ICD-10 codes. Any claims submitted for Outpatient services with a date of service or Inpatient discharges with a discharge date on or after October 1, 2013 must be submitted using ICD-10 codes to avoid immediate denial. Claims that were denied due to use of ICD-9 codes will need to be resubmitted using ICD-10 codes .
Everyone will need to either convert or map existing systems over to use the new ICD-10 codes well in advance of the October transition date .
Changing from ICD-9 to ICD-10 will not only require changes to coding systems, but billing systems as well. The current HIPAA transaction standards for electronic health care transactions, such as claims processing systems, will change from version 4010/4010A1 to Version 5010. Health plans, healthcare clearing houses, and providers are impacted by this change. Any system used or claims processing, remittance advice, claim status inquiry, or eligibility inquiry must be adapted to accommodate the new ICD-10 format .
This transition will occur on January 1, 2012, well ahead of the ICD-10 transition date. Transactions from non-compliant systems will be rejected as of January 1, 2012 .
Hospitals that have converted to native ICD-10 codes will see minimal impact in reimbursements. However, hospitals that have chosen to map ICD-9 to ICD-10 codes may encounter problems with reimbursement due to differences with interpretation of codes used in mapping .
The overall cost of converting to ICD-10 is substantial due effort involved in changing systems, hiring technical staff/consultants, and training employees. According to RAND estimates, the benefits over 10 years may exceed $7 billion and far outweigh the costs. Mapping applications for backwards compatibility is less costly initially, however, the benefits are not predictable and maintaining application compatibility will be problematic .
- See also Transitioning from ICD-9 to ICD-10
- "Overview ICD-10." Centers for Medicare & Medicaid Services. Web. 27 Feb. 2011. .
- USA. Centers for Medicare & Medicaid Services (CMS). New Health Care Electronic Transactions Standards Versions 5010, D.0, and 3.0. Vol. ICN 903192. January 2010. Print.
- "Version 5010 ICD-10." Centers for Medicare & Medicaid Services. Web. 27 Feb. 2011. .
- Mills, Ronald E., Rhonda R. Butler, Richard F. Averill, Elizabeth C. McCullough, and Mona Z. Bao. Impact of the Transition to ICD-10 on Medicare Inpatient Hospital Payments. Tech. Wallingford, Connecticut: 3M Health Information Systems. Print.
- Converting MS-DRGs 26.0 to ICD-10-CM and ICD-10-PCS Page 6. 
Submitted by Kenneth Gridley
- Federal Register, Vol. 74, No. 11, Friday, January 16, 2009.
- Analysis of the Final Rule: HIPAA Administrative Simplification: Modification to Medical Data Code Set Standards to Adopt ICD-10-CM and ICD-10-PCS, AHIMA, January 2009.
- Giannangelo, Kathy, ed. Health Code Sets, Clinical Terminologies, and Classification Systems. Chicago: AHIMA, 2006.
June 2012 Update
Comparing ICD-9-CM to ICD-10-CM/PCS
The ICD-10-CM is a clinical modification of the ICD-10 made for the United States and approved by the World Health Organization, which holds the copyright. It consists of two volumes, an index and a tabular listing, that provide codes for diagnoses for all healthcare encounters. This mirrors the previous version of ICD-9-CM volumes 1 and 2 with a few alterations in structure. The differences between these two structures are outlined below:
|3-5 characters||3-7 characters|
|primarily numeric (except V&E codes)||Character 1 is alpha (A-Z except U)|
|4th and 5th digits afford additional specificity||Character 2 is numeric|
|(but generalized by comparison to ICD-10)||Character 3-7 is alpha or numeric|
|Does not provide for laterality||Codes distinguish laterality|
|Not all codes have full description||All codes have full description|
(Zeissert and Bowman, 2010)
ICD-10-PCS is a completely new coding structure developed by the Centers for Medicare and Medicaid Services (CMS) that replaces the ICD-9-CM volume 3 to report codes for inpatient procedures only. ICD-9-CM procedure codes consisted of a very simple 2-3 character code that covered general surgical procedures, describing very little detail. ICD-10-PCS provides a classification system based on various coding axes such as type of service, i.e. medical, surgical, obstetric, etc., body area/system, root operation, approach, devices and other descriptors. (Averill, 2001) This new system is a vast departure from what physicians and coders are used to and will require the most amount of training for hospitals to become compliant with accurate PCS reporting. Providers and staff must learn the new terminology and definitions that come with the 31 root operations, words that have often been used to describe one thing will now be used for another. (Zeissert and Bowman, 2010) For example, the root operation “resection” is defined as “cutting off or out, without replacement, all of a body part”. In the current medical vernacular, the term “resection” is often used to describe cutting either an entire body part or a portion. This will obviously become important when coding in ICD-10-PCS.
Much has been discussed about the financial impact on hospital and physicians to get ready for the implementation of ICD-10-CM/PCS as well as the potential savings that might be realized down the road. The AMA has vigorously fought against the October 1, 2013 implementation deadline and wrote a letter to the Acting Secretary of Health and Human Services, Kathleen Sebelius, asking that the deadline be rolled back and/or the transition to ICD-10 be foregone altogether. (Madera 2012) In a move that surprised many HIM professionals, HHS proposed a final rule to extend the implementation date to October 1, 2014. (CMS 2012) While this may delay some costs for some physicians, most larger facilities and health insurance companies have already invested millions of dollars in infrastructure and training to prepare for the original date. This year delay could actually cause a loss for those that now have to retrain or invest in additional spending to support software contracts for services related to ICD-10 that they will not use for another year. (Averill and Bowman, 2012)
- Averill RF, Mullin RL, Steinbeck BA, Goldfield NI, Grant TM. Development of the ICD-10 procedure coding system (ICD-10-PCS). Top Health Inf Manage. 2001 Feb;21(3):54-88. Zeissert A, Bowman S. Pocket Guide of ICD-10-CM and ICD-10-PCS. Chicago, American Health Information Management Association, 2010.
- Madera J. [internet] Letter to HHS, February 2, 2012. [cited May 31, 2012]. 
- CMS Office of Public Affairs. [internet] HHS proposes one year delay of ICD-10 compliance date. [cited May 31, 2012] CMS.gov, 2012. 
- Averill R, Bowman S. There Are Critical Reasons for Not Further Delaying the Implementation of the New ICD-10 Coding System. J of AHIMA, 2012: (83)1-9.
Submitted by JoAnn Jordan, MPH