International Classification of Diseases (ICD)
The International Statistical Institute gave a committee headed by Dr. Jacques Bertillon (1851-1922) the
task of drawing up a classification of diseases. This committee presented its report in 1893 at Chicago.
This classification system was based on one revised in 1885 and used by the City of Paris, which was
itself a mixture of English, German and Swiss classifications. Bertillon's Classification was in three
separate forms:
 a short classification with 44 titles,
 a second classification with 99 titles, and
 a third classification with 161 titles.
The first revision (ICD1) was produced by Bertillon in 1900 and had 192 codes, one of which was a
subdivision. Further revisions under Bertillon were produced in 1910 and 1920; the coding was revised
again in 1929 and 1938.
With the sixth revison in 1948 new opportunities were taken with the approval of a comprehensive list
for both mortality and morbidity; an International set of rules for determining 'Underlying Cause of
Death' was agreed. The seventh revision under the World Health Organisation came in 1955.
The eighth revision came in 1965 (ICD8) now clearly dividing diseases into chapters, grouping main
diseases together with three digit codes, a fourth digit allowed further detail of the conditions to be
recorded. Thus Chapter VII is headed 'Diseases of the Circulatory System' and is coded between 390
and 459. Within this, code 441 shows the main heading for this coding as 'Aortic Aneurysm (nonsyphilitic)' with subdivision 0 (441.0) as 'Dissecting aneurysm of aorta (any part), subdivision 1 (441.1)
as 'Thoracic', while subdivision 2 (441.2) refers to an Abdominal Aortic Aneurysm.
LS data for 1971 to 1980 uses ICD8 codes. The ninth revision (ICD9) came in 1975 and was adopted
for LS use from 1981. Both revisions eight and nine had seventeen chapters, however revision nine
codes could be more finely divided and not all major headings corresponded (e.g. 264 and 265), care
must therefore be taken when grouping disease codes from different ICD revisions to ensure that they
match correctly.
In the LS the ICD9 code is stored in two variables: ucde3dde (first 3 digits) and ucdexdde (fourth digit)
until 1993 when a new variable (icd9ude) was introduced which holds all four digits of the relevant
code.
ICD10 was endorsed by WHO in 1990 and adopted for use in 1994 but did not come into use in the LS
until 2001. ICD10 has twenty two chapters and a completely different alpha-numeric coding system. An
initial letter is followed by two digits giving a main classification, a third digit then further subdivides
the disease.
As an example: codes I10 to I15 represent Hypertensive diseases and I13.1 is specifically Hypertensive
heart and renal disease with renal failure. Users of the LS should be aware that the decimal point shown
here is not used and the stored code in this case would be I131.
It was agreed, when preparing the 10th edition, that 10 years between revisions was not long enough for
the previous revision to 'prove itself', or for its advantages and shortcomings really to reveal themselves.
ICD10 has been updated a number of times to take account of new conditions / diseases as they have
become recognised. However the main body of the ICD10 classification has remained unchanged.