The International Classification of Diseases (ICD) set code is the international standard diagnostic tool for epidemiology, health management and clinical purposes. ICD codes are maintained by the World Health Organization, the directing and coordinating authority for health within the United Nations System.

The most current version is ICD-10, which replaced ICD-9 on Oct. 15, 2015.

ICD-10 was originally issued in 1992 by the WHO. It has been adopted by most developed nations. Thus, the United States is one of the last developed nations to adopt ICD-10.

ICD-11 is scheduled to be released during 2018. A beta version of ICD-11 has been available online since 2012. Countries around the world that have used ICD-10 for more than two decades are expected to move expeditiously to adopt ICD-11.

The ICD is designed as a health care classification system, providing a system of diagnostic codes for classifying diseases, including nuanced classifications of a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease.

ICD codes are used by clinical laboratories for billing purposes, and by physicians, nurses, other providers, researchers, health information managers and coders, health information technology workers, policy-makers, insurers and patient organizations to classify diseases and other health problems recorded on many types of health and vital records, including death certificates and health records.

In addition to enabling the storage and retrieval of diagnostic information for clinical, epidemiological and quality purposes, these records also provide the basis for the compilation of national mortality and morbidity statistics by WHO Member States. Finally, ICD is used for reimbursement and resource allocation decision-making by countries.

Clinical laboratories and pathology groups have a big stake in successful transition to ICD-10. Medicare Part B claims for medical laboratory tests must be submitted with an appropriate ICD code provided by the physicians who ordered the lab tests. Lab test claims without an appropriate ICD code will not be reimbursed by the Medicare program.