INTERNATIONAL CLASSIFICATION OF DISEASES
Certain rubrics contain lists of conditions preceded by the word “Excludes”. These are terms which,
although the rubric title might suggest that they were to be classified there, are in fact classified
elsewhere. An example of this is in category A46, “Erysipelas”, where postpartum or puerperal
erysipelas is excluded. Following each excluded term, in parentheses, is the category or subcategory
code elsewhere in the classification to which the excluded term should be allocated.
General exclusions for a range of categories or for all subcategories in a three-character category are to
be found in notes headed “Excludes”, immediately following a chapter, block or category title.
In addition to inclusion and exclusion terms, Chapter V, Mental and behavioural disorders, uses
glossary descriptions to indicate the content of rubrics. This device is used because the terminology of
mental disorders varies greatly, particularly between different countries, and the same name may be
used to describe quite different conditions. The glossary is not intended for use by coding staff.
Similar types of definition are given elsewhere in the ICD, for example, Chapter XXI, to clarify the
intended content of a rubric.
3.1.3 Two codes for certain conditions
The “dagger and asterisk” system
ICD-9 introduced a system, continued in ICD-10, whereby there are two codes for diagnostic
statements containing information about both an underlying generalized disease and a manifestation in
a particular organ or site which is a clinical problem in its own right.
The primary code is for the underlying disease and is marked with a dagger (†); an optional additional
code for the manifestation is marked with an asterisk (*). This convention was provided because
coding to underlying disease alone was often unsatisfactory for compiling statistics relating to
particular specialties, where there was a desire to see the condition classified to the relevant chapter for
the manifestation when it was the reason for medical care.
While the dagger and asterisk system provides alternative classifications for the presentation of
statistics, it is a principle of the ICD that the dagger code is the primary code and must always be used.
Provision should be made for the asterisk code to be used in addition if the alternative method of
presentation may also be required. For coding, the asterisk code must never be used alone. Statistics
incorporating the dagger codes conform with the traditional classification for presenting data on
mortality and morbidity and other aspects of medical care.
Asterisk codes appear as three-character categories. There are separate categories for the same
conditions occurring when a particular disease is not specified as the underlying cause. For example,
categories G20 and G21 are for forms of Parkinsonism that are not manifestations of other diseases
assigned elsewhere, while category G22
is for “Parkinsonism in diseases classified elsewhere”.
Corresponding dagger codes are given for conditions mentioned in asterisk categories; for example,
for Syphilitic parkinsonism in G22
, the dagger code is A52.1†.
Some dagger codes appear in special dagger categories. More often, however, the dagger code for
dual-element diagnoses and unmarked codes for single-element conditions may be derived from the
same category or subcategory.
The areas of the classification where the dagger and asterisk system operates are limited; there are 83
special asterisk categories throughout the classification, which are listed at the start of the relevant
HOW TO USE THE ICD
Rubrics in which dagger-marked terms appear may take one of three different forms:
If the symbol (†) and the alternative asterisk code both appear in the rubric heading, all terms
classifiable to that rubric are subject to dual classification and all have the same alternative
A17.0† Tuberculous meningitis (G01
Tuberculosis of meninges (cerebral) (spinal)
If the symbol appears in the rubric heading but the alternative asterisk code does not, all terms
classifiable to that rubric are subject to dual classification but they have different alternative
codes (which are listed for each term), e.g.
A18.1† Tuberculosis of genitourinary system
male genital organs (N51.-
Tuberculous female pelvic inflammatory disease (N74.1
(iii) If neither the symbol nor the alternative code appear in the title, the rubric as a whole is not
subject to dual classification but individual inclusion terms may be; if so, these terms will be
marked with the symbol and their alternative codes given, e.g.
A54.8 Other gonococcal infections
Other optional dual coding
There are certain situations, other than in the dagger and asterisk system, that permit two ICD codes to
be used to describe fully a person’s condition. The note in the tabular list, “Use additional code, if
desired ...”, identifies many of these situations. The additional codes would be used only in special
for local infections, classifiable to the “body systems” chapters, codes from Chapter I may be
added to identify the infecting organism, where this information does not appear in the title of
the rubric. A block of categories, B95-B97, is provided for this purpose in Chapter I.
for neoplasms with functional activity. To the code from Chapter II may be added the
appropriate code from Chapter IV to indicate the type of functional activity.
(iii) for neoplasms, the morphology code from Volume 1, although not part of the main ICD, may
be added to the Chapter II code to identify the morphological type of the tumour.
for conditions classifiable to F00-F09 (Organic, including symptomatic, mental disorders) in
Chapter V, where a code from another chapter may be added to indicate the cause, i.e. the
underlying disease, injury or other insult to the brain.
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INTERNATIONAL CLASSIFICATION OF DISEASES
where a condition is caused by a toxic agent, a code from Chapter XX may be added to
identify that agent.
where two codes can be used to describe an injury, poisoning or other adverse effect: a code
from Chapter XIX, which describes the nature of the injury, and a code from Chapter XX,
which describes the cause. The choice as to which code should be the additional code depends
upon the purpose for which the data are being collected. (See introduction to Chapter XX, of
3.1.4 Conventions used in the tabular list
In listing inclusion and exclusion terms in the tabular list, the ICD employs some special conventions
relating to the use of parentheses, square brackets, colons, braces, the abbreviation “NOS”, the phrase
“not elsewhere classified” (NEC), and the word “and” in titles. These need to be clearly understood
both by coders and by anyone wishing to interpret statistics based on the ICD.
Parentheses ( )
Parentheses are used in Volume 1 in four important situations.
Parentheses are used to enclose supplementary words, which may follow a diagnostic term
without affecting the code number to which the words outside the parentheses would be
assigned. For example, in I10 the inclusion term, “Hypertension (arterial) (benign) (essential)
(malignant) (primary) (systemic)”, implies that I10 is the code number for the word
“Hypertension” alone or when qualified by any, or any combination, of the words in
Parentheses are also used to enclose the code to which an exclusion term refers. For example,
Excludes: blepharoconjunctivitis (H10.5).
Another use of parentheses is in the block titles, to enclose the three-character codes of
categories included in that block.
The last use of parentheses was incorporated in the Ninth Revision and is related to the dagger
and asterisk system. Parentheses are used to enclose the dagger code in an asterisk category or
the asterisk code following a dagger term.
Square brackets [ ]
Square brackets are used:
for enclosing synonyms, alternative words or explanatory phrases; for example,
A30 Leprosy [Hansen’s disease];
for referring to previous notes; for example,
C00.8 Overlapping lesion of lip [See note 5 at the beginning of this chapter];
for referring to a previously stated set of fourth character subdivisions common to a number of
categories; for example,
K27 Peptic ulcer, site unspecified [See before K25 for subdivisions].
A colon is used in listings of inclusion and exclusion terms when the words that precede it are not
complete terms for assignment to that rubric. They require one or more of the modifying or qualifying
words indented under them before they can be assigned to the rubric. For example, in K36, “Other
HOW TO USE THE ICD
appendicitis”, the diagnosis “appendicitis” is to be classified there only if qualified by the words
“chronic” or “recurrent”.
A brace is used in listings of inclusion and exclusion terms to indicate that neither the words that
precede it nor the words after it are complete terms. Any of the terms before the brace should be
qualified by one or more of the terms that follow it. For example:
O71.6 Obstetric damage to pelvic joints and ligaments
Avulsion of inner symphyseal cartilage
Damage to coccyx
Traumatic separation o
f symphysis (pubis)
The letters NOS are an abbreviation for “not otherwise specified”, implying “unspecified” or
Sometimes an unqualified term is nevertheless classified to a rubric for a more specific type of the
condition. This is because, in medical terminology, the most common form of a condition is often
known by the name of the condition itself and only the less common types are qualified. For example,
“mitral stenosis” is commonly used to mean “rheumatic mitral stenosis”. These inbuilt assumptions
have to be taken into account in order to avoid incorrect classification. Careful inspection of inclusion
terms will reveal where an assumption of cause has been made; coders should be careful not to code a
term as unqualified unless it is quite clear that no information is available that would permit a more
specific assignment elsewhere. Similarly, in interpreting statistics based on the ICD, some conditions
assigned to an apparently specified category will not have been so specified on the record that was
coded. When comparing trends over time and interpreting statistics, it is important to be aware that
assumptions may change from one revision of the ICD to another. For example, before the Eighth
Revision, an unqualified aortic aneurysm was assumed to be due to syphilis.
“Not elsewhere classified”
The words “not elsewhere classified”, when used in a three-character category title, serve as a warning
that certain specified variants of the listed conditions may appear in other parts of the classification.
Pneumonia due to other infectious organisms, not elsewhere classified
This category includes J16.0 Chlamydial pneumonia and J16.8 Pneumonia due to other specified
infectious organisms. Many other categories are provided in Chapter X (for example, J10-J15) and
other chapters (for example, P23.- Congenital pneumonia) for pneumonias due to specified infectious
organisms. J18 Pneumonia, organism unspecified, accommodates pneumonias for which the infectious
agent is not stated.
“And” in titles
“And” stands for “and/or”. For example, in the rubric A18.0, Tuberculosis of bones and joints, are to
be classified cases of “tuberculosis of bones”, “tuberculosis of joints” and “tuberculosis of bones and
INTERNATIONAL CLASSIFICATION OF DISEASES
In some cases, the fourth character of a subcategory code is replaced by a dash, e.g.
G03 Meningitis due to other and unspecified causes,
Excludes: meningoencephalitis (G04.-)
This indicates to the coder that a fourth character exists and should be sought in the appropriate
category. This convention is used in both the tabular list and the alphabetical index.
3.1.5 Categories with common characteristics
For quality control it is useful to introduce programmed checks into the computer system. The
following groups of categories are provided as a basis for such checks on internal consistency,
grouped according to the special characteristic that unites them.
The following asterisk categories are not to be used alone; they must always be used in addition to a
Categories limited to one sex
The following categories apply only to males:
B26.0, C60-C63, D07.4-D07.6, D17.6, D29.-, D40.-, E29.-, E89.5, F52.4, I86.1, L29.1, N40-N51,
Q53-Q55, R86, S31.2-S31.3, Z12.5.
The following categories apply only to females:
A34, B37.3, C51-C58, C79.6, D06.-, D07.0-D07.3, D25-D28, D39.-, E28.-, E89.4, F52.5, F53.-,
I86.3, L29.2, L70.5, M80.0-M80.1, M81.0-M81.1, M83.0, N70-N98, N99.2-N99.3, O00-O99, P54.6,
Q50-Q52, R87, S31.4, S37.4-S37.6, T19.2-T19.3, T83.3, Y76.-, Z01.4, Z12.4, Z30.1, Z30.3, Z30.5,
Z31.1, Z31.2, Z32-Z36, Z39.-, Z43.7, Z87.5, Z97.5.
Guidance for handling inconsistencies between conditions and sex is given at 4.2.5.
The following categories are provided for sequelae of conditions that are no longer in an active phase:
B90-B94, E64.-, E68, G09, I69.-, O97, T90-T98, Y85-Y89.
Guidance for coding sequelae for both mortality and morbidity purposes can be found at 4.2.4 and
The following categories are not to be used for underlying-cause mortality coding. Guidance for their
use in morbidity coding is found at 4.4.2.
E89.-, G97.-, H59.-, H95.-, I97.-, J95.-, K91.-, M96.-, N99.-.
HOW TO USE THE ICD
3.2 How to use Volume 3
The Introduction to Volume 3, the Alphabetical Index to ICD-10, gives instructions on how to use it.
These instructions should be studied carefully before starting to code. A brief description of the
structure and use of the Index is given below.
3.2.1 Arrangement of the Alphabetical Index
Volume 3 is divided into three sections as follows:
Section I lists all the terms classifiable to Chapters I-XIX and Chapter XXI, except drugs and other
Section II is the index of external causes of morbidity and mortality and contains all the terms
classifiable to Chapter XX, except drugs and other chemicals.
Section III, the Table of Drugs and Chemicals, lists for each substance the codes for poisonings and
adverse effects of drugs classifiable to Chapter XIX, and the Chapter XX codes that indicate
whether the poisoning was accidental, deliberate (self-harm), undetermined, or an adverse effect of
a correct substance properly administered.
The Index contains “lead terms”, positioned to the far left of the column, with other words
(“modifiers” or “qualifiers”) at different levels of indentation under them. In Section I, these indented
modifiers or qualifiers are usually varieties, sites or circumstances that affect coding; in Section II they
indicate different types of accident or occurrence, vehicles involved, etc. Modifiers that do not affect
coding appear in parentheses after the condition.
3.2.3 Code numbers
The code numbers that follow the terms refer to the categories and subcategories to which the terms
should be classified. If the code has only three characters, it can be assumed that the category has not
been subdivided. In most instances where the category has been subdivided, the code number in the
Index will give the fourth character. A dash in the fourth position (e.g. O03.-) means that the category
has been subdivided and that the fourth character can be found by referring to the tabular list. If the
dagger and asterisk system applies to the term, both codes are given.
Parentheses are used in the Index in the same way as in Volume 1, i.e. to enclose modifiers.
NEC (not elsewhere classified) indicates that specified variants of the listed condition are classified
elsewhere, and that, where appropriate, a more precise term should be looked for in the Index.
Cross-references are used to avoid unnecessary duplication of terms in the Index. The word “see”
requires the coder to refer to the other term; “see also” directs the coder to refer elsewhere in the Index
if the statement being coded contains other information that is not found indented under the term to
which “see also” is attached.
3.3 Basic coding guidelines
The Alphabetical Index contains many terms not included in Volume 1, and coding requires that both
the Index and the Tabular List should be consulted before a code is assigned.
INTERNATIONAL CLASSIFICATION OF DISEASES
Before attempting to code, the coder needs to know the principles of classification and coding and to
have carried out practical exercises.
The following is a simple guide intended to assist the occasional user of the ICD.
1. Identify the type of statement to be coded and refer to the appropriate section of the Alphabetical
Index. (If the statement is a disease or injury or other condition classifiable to Chapters I - XIX or
XXI, consult Section I of the Index. If the statement is the external cause of an injury or other
event classifiable to Chapter XX, consult Section II.)
2. Locate the lead term. For diseases and injuries this is usually a noun for the pathological
condition. However, some conditions expressed as adjectives or eponyms are included in the
Index as lead terms.
3. Read and be guided by any note that appears under the lead term.
4. Read any terms enclosed in parentheses after the lead term (these modifiers do not affect the code
number), as well as any terms indented under the lead term (these modifiers may affect the code
number), until all the words in the diagnostic expression have been accounted for.
5. Follow carefully any cross-references (“see” and “see also”) found in the Index.
6. Refer to the tabular list to verify the suitability of the code number selected. Note that a
three-character code in the Index with a dash in the fourth position means that there is a fourth
character to be found in Volume 1. Further subdivisions to be used in a supplementary character
position are not indexed and, if used, must be located in Volume 1.
7. Be guided by any inclusion or exclusion terms under the selected code or under the chapter, block
or category heading.
8. Assign the code.
Specific guidelines for the selection of the cause or condition to be coded, and for coding the condition
selected, are given in Section 4.
4. Rules and guidelines for mortality and morbidity
This section concerns the rules and guidelines adopted by the World Health Assembly regarding the
selection of a single cause or condition for routine tabulation from death certificates and morbidity
records. Guidelines are also provided for the application of the rules and for coding of the condition
selected for tabulation.
4.1 Mortality: guidelines for certification and rules for coding
Mortality statistics are one of the principal sources of health information and in many countries they
are the most reliable type of health data.
4.1.1 Causes of death
In 1967, the Twentieth World Health Assembly defined the causes of death to be entered on the
medical certificate of cause of death as “all those diseases, morbid conditions or injuries which either
resulted in or contributed to death and the circumstances of the accident or violence which produced
any such injuries”. The purpose of the definition is to ensure that all the relevant information is
recorded and that the certifier does not select some conditions for entry and reject others. The
definition does not include symptoms and modes of dying, such as heart failure or respiratory failure.
When only one cause of death is recorded, this cause is selected for tabulation. When more than one
cause of death is recorded, selection should be made in accordance with the rules given in section
4.1.5. The rules are based on the concept of the underlying cause of death.
4.1.2 Underlying cause of death
It was agreed by the Sixth Decennial International Revision Conference that the cause of death for
primary tabulation should be designated the underlying cause of death.
From the standpoint of prevention of death, it is necessary to break the chain of events or to effect a
cure at some point. The most effective public health objective is to prevent the precipitating cause
from operating. For this purpose, the underlying cause has been defined as “(a) the disease or injury
which initiated the train of morbid events leading directly to death, or (b) the circumstances of the
accident or violence which produced the fatal injury”.
4.1.3 International form of medical certificate of cause of death
The above principle can be applied uniformly by using the medical certification form recommended
by the World Health Assembly. It is the responsibility of the medical practitioner signing the death
certificate to indicate which morbid conditions led directly to death and to state any antecedent
conditions giving rise to this cause.
The medical certificate shown below is designed to facilitate the selection of the underlying cause of
death when two or more causes are recorded. Part I of the form is for diseases related to the train of
events leading directly to death, and Part II is for unrelated but contributory conditions.
INTERNATIONAL CLASSIFICATION OF DISEASES
The medical practitioner or other qualified certifier should use his or her clinical judgement in
completing the medical certificate of cause of death. Automated systems must not include lists or other
prompts to guide the certifier as these necessarily limit the range of diagnoses and therefore have an
adverse effect on the accuracy and usefulness of the report.
In 1990, the Forty-third World Health Assembly adopted a recommendation that, where a need had
been identified, countries should consider the possibility of an additional line, (d), in Part I of the
certificate. However, countries may adopt, or continue to use, a certificate with only three lines in Part
I where a fourth line is unnecessary, or where there are legal or other impediments to the adoption of
the certificate shown above.
The condition recorded on the lowest used line of Part I of the certificate is usually the underlying
cause of death used for tabulation. However, the procedures described in sections 4.1.4-4.1.5 may
result in the selection of another condition as the underlying cause of death. To differentiate between
these two possibilities, the expression originating antecedent cause (originating cause) will be used to
refer to the condition proper to the last used line of Part I of the certificate, and the expression
underlying cause of death will be used to identify the cause selected for tabulation.
If there is only one step in the chain of events, an entry at line I(a) is sufficient. If there is more than
one step, the direct cause is entered at (a) and the originating antecedent cause is entered last, with any
intervening cause entered on line (b) or on lines (b) and (c). An example of a death certificate with
four steps in the chain of events leading directly to death is:
(a) Pulmonary embolism
(b) Pathological fracture
(c) Secondary carcinoma of femur
(d) Carcinoma of breast
Part II is for any other significant condition that contributed to the fatal outcome, but was not related
to the disease or condition directly causing death.
After the words “due to (or as a consequence of)”, which appear on the certificate, should be included
not only the direct cause or pathological process, but also indirect causes, for example where an
antecedent condition has predisposed to the direct cause by damage to tissues or impairment of
function, even after a long interval.
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