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Changes in the classification of disease

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The main changes to the classification of diseases between ICD-9 and ICD-10 are given below, with some examples:

  • Changes to the number and structure of Chapters

  • There are now 20 Chapters instead of 18.

  • The nervous system and sense organs chapter from ICD-9 has been split into 3 Chapters - nervous system (VI), eye and adnexa (VII), and ear and mastoid process (VIII).

  • Chapters III and IV have changed order and "certain disorders of the immune mechanism" moved from the endocrine chapter (now Chapter IV) to the blood Chapter (now Chapter III).

  • Movement of conditions between ICD Chapters

  • Certain "disorders of blood" have moved from the blood Chapter (III) to the neoplasms Chapter (II).

  • New codes for conditions not previously identified separately in the ICD

  • Mesothelioma and Kaposi's sarcoma now have their own codes.

  • Changes in the code assigned to a term in the ICD index (volume III)

  • Changes in the inclusion and exclusion notes in the tabular list of the ICD (volume I)

  • Changes in linkages between conditions (given in volume II of the ICD)

  • Expansion of categories for more detailed classification of conditions of increasing importance

  • HIV/AIDS has an expanded number of codes in ICD-10 (B20-B24).

  • The detail given about acute myocardial infarction has been increased, with many codes used in ICD-10 where only one had been used in ICD-9.

  • Collapsing of categories where distinctions are no longer relevant

  • Autoimmune disease and connective tissue disease are given the same code in ICD-10, rather than separate ones as they were in ICD-9

More details on these changes can be found in Health Statistics Quarterly 13

These changes are not the only ones to affect cause of death statistics. There have also been changes in the underlying cause of death selection and modification rules.

Both these sets of changes have resulted in deaths being coded to different causes of death in ICD-10 compared to ICD-9.

Content from the Office for National Statistics.
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