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The International Statistical Classification of Diseases and Related Health Problems 10th Revision (ICD-10) is produced and maintained by the World Health Organisation (WHO). It was first mandated for use in the UK in 1995. The purpose of ICD-10 is to permit the systematic recording, analysis, interpretation and comparison of mortality and morbidity data collected in different countries or areas and at different times. ICD-10 is used to translate diagnoses of diseases and other health problems from words (as described by a clinician) into an alphanumeric code which permits easy storage, retrieval and analysis of that data. Since 1995 it has been updated (see below) in order to keep pace with the continually evolving medical information that it records.


ICD-10 Updates:

  • 2016: ICD-10 5th Edition - implemented in Wales effective from 1st April 2016.

  • 2012: ICD-10 4th Edition – implemented in Wales effective from 1stJuly 2012.

  • 2004: ICD-10 reprinted with updates and corrections – implemented in Wales effective from 1st April 2004.

  • 1995: ICD-10 – implemented in Wales effective from 1st August 1994.


ICD-10 is:

  • statistical classification designed for international comparisons of mortality and morbidity.

  • A classification which is based on grouping categories chosen to facilitate the statistical study of disease phenomena.

  • statistical tool used to study the epidemiology of populations.

  • A tool which requires knowledge and understanding of its purpose and structure by statisticians and analysts of health information, as well as by coders

  • Based on rules which include the definition of the primary diagnosis as:

    i. “The first diagnosis field(s) of the coded clinical record (the primary diagnosis) will contain the main condition treated or investigated during the relevant episode of healthcare”

    ii. “Where a definitive diagnosis has not been made by the responsible clinician the main symptom, abnormal findings or problem should be recorded in the first diagnosis field of the coded clinical record.”


ICD-10 is not:

  • A tool to support direct patient care which enables clinicians to comprehensively record all relevant patient health problems in encoded format.

  • It is not intended for indexing of distinct clinical entities as it is not a nomenclature designed to describe all possible morbid conditions as these must have a separate name for each morbid condition.

  • It is not designed to describe the health status of an individual patient, as it is not, for example:

    o Capable of attributing levels of certainty to a diagnosis;

    o Capable of attributing levels of severity to a diagnosis;

    o Capable of attributing negativity, i.e. possibly relevant diagnoses which have been excluded by clinicians.


Sally Greenway, former Head of Information Standards (Welsh Government) has developed an ‘ICD-10 Essentials’ briefing paper, further describing the uses and limitations of the ICD-10 classification. It can be accessed via the following link: ICD-10 Essentials.