ICD-10 Rules and Conventions

Question 1

Where do Rules apply throughout the classification?

How are they identified within the ICD-10 reference book?

Answer 1

Rules of ICD-10 apply throughout the classification and the clinical coder must be aware of
these rules in order to code with consistency and accuracy.
A rule that a coder must comply with is presented in a grey box. Explanatory information
about the rule is presented in a white box.
The unique identifiers for rules begin with ‘DRule’ and are followed by the number of the rule
and the title (e.g. DRule.2: Category and code structure).

Question 2

Where do Conventions apply throughout the classification?

How are they identified within the ICD-10 reference book?

Answer 2

Conventions of ICD-10 are fundamental to accurate coding and apply throughout the
classification (including the Alphabetical Index).
The clinical coder must thoroughly understand these conventions and always apply them to
ensure correct code assignment and sequencing.
The unique identifiers for conventions begin with ‘DConvention’ followed by the number of
the convention and the title (e.g. DConvention.1: Cross references).

Question 3

Fully describe DRule.1: Axis of the classification and rules of chapter prioritisation

Answer 3

Where there is any doubt as to where a condition should be coded, the ‘special group’
chapters must take priority.

The ICD is a variable-axis classification. Its 22 chapters are divided into the following three
types:

Special group chapters
Chapters I-V, XV-XVII and XIX classify conditions that do not focus on any one body
system. In general, conditions are primarily classified to one of the ‘special group’
chapters.

Body system chapters
Chapters VI-XIV classify conditions according to the body system they affect.

Other chapters
Chapters XVIII and XX-XXII classify other disorders and factors which do not sit
comfortably in either a special group or body system chapter.

Question 4

Fully describe DRule.2: Category and code structure

Answer 4

Code assignment must always be made to four character level or five character level
(where available and in line with fifth character coding standards), in order for the code to
be valid.

Where a three character category code is not subdivided into four character subdivisions
the ‘X’ filler must be assigned in the fourth character field so the codes are of a standard
length for data processing and validation. The code is still considered a three character
code from a classification perspective.

Where a three character code requires assignment of both the ‘X’ filler and a fifth character
subdivision, the ‘X’ filler must continue to be recorded in the fourth field before the fifth
character, for example M45.X3 Ankylosing spondylitis, cervicothoracic region.
See also DConvention.7: Fifth characters.

Question 5

How many types of cross reference are there in the ICD-10 Alphabetical Index?

Answer 5

Two

Question 6

Describe the cross references defined in DConvention.1: Cross references

Answer 6

See

This is an explicit direction to look elsewhere as no codes can be found alongside this
cross reference. It is used to direct the coder to another lead term in the Alphabetical Index
where complete information can be found. It is also used after anatomical sites to remind
the coder that the Alphabetical Index is organised by condition.

See also

This is a reminder to look under another lead term if the term the coder is looking for
cannot be found modified in any way under the first lead term.

Question 7

What are cross references?

Answer 7

Cross references are provided in the Alphabetical Index to ensure that all possible terms or
its synonyms are referenced by the coder. Cross references explicitly direct the coder to
other entries in the index:

Question 8

DConvention.2: Instructional notes

What are Instructional notes?

Answer 8

Instructional ‘Notes’ are used within the Tabular list at chapter level, block level, threecharacter
and four-character levels. They describe the general content of the succeeding
categories, give instruction regarding the use of categories and provide fifth character subclassifications.

Question 9

DConvention.2: Instructional notes

What are Inclusion notes?

Answer 9

Inclusion notes clarify the content and intended use of the chapter, block, category or
subcategory to which the notes apply. They give examples of the conditions and diagnoses
classified at the chapter, block, category or code. The listed inclusion terms are not
exhaustive and alternative diagnoses are listed in the Alphabetical Index.

Inclusion notes appearing under chapter and block titles usually give a general definition of
the content of the section to which they apply. These inclusion notes apply to all categories
within the chapter or block.

Inclusion notes at four character code level are not preceded by the abbreviation Incl.:

Question 10

DConvention.2: Instructional notes

What are Exclusion notes?

Answer 10

Exclusion notes (exclusion terms, ‘Excl.:’)
Exclusion notes are used to prevent a category or code from being used incorrectly:

• They inform the coder that, although the category or code description may suggest
the term could be classified here, it is in fact classified elsewhere,
however
• They do not always prevent the use of the code from the category the exclusion
note appears in; they can indicate that a code from a different category should be
assigned in addition to fully reflect the patient’s diagnoses.

Question 11

DConvention.2: Instructional notes

What are use notes?

Answer 11

The ‘use’ note is a specific instruction to use an additional code in order to describe a
condition more completely and, just like other types of notes, can be found at chapter,
block, three character category and fourth character subcategory levels. The ‘use’ note is
never optional and must always be adhered to where the information is available in the
medical record.

Question 12

DConvention.2: Instructional notes

What are if desired notes?

Answer 12

Where a note states to ‘Use an additional code, if desired’ to add further information about
the disorder, where that information is present in the medical record the additional code
must be assigned.

Question 13

DConvention.2: Instructional notes

What are ‘are for use with’ notes?

Answer 13

Where a note contains the phrase ‘are for use with’, this instruction is mandatory, and the
four-character subdivisions referred to must be used

Question 14

DConvention.3: Punctuation name the five types of punctuation found within the ICD-10 Classification

Answer 14

Brace |
Square brackets [ ]
Colon :
Point dash .–
Parentheses ( )

Question 15

DConvention.3: Punctuation define a Brace |

Answer 15

Braces (indicated by a vertical line in the Tabular List) are used in inclusion and exclusion
notes to indicate that both the listed condition and one of its modifiers must be present in
order to complete the instruction. Braces enclose a series of terms, modified by the
statement appearing at the right of the brace.

Question 16

DConvention.3: Punctuation when are Square brackets [ ] used

Answer 16

Square brackets are used to:
• enclose synonyms, alternative words, or explanatory phrases
• enclose an instruction to ‘see’ previously listed subdivisions common to a number of
categories
• refer to a previous ‘see’ note.

Question 17

DConvention.3: Punctuation wher can you find a Colon :

Answer 17

A colon is used above a list of bulleted modifiers (•) in the Tabular List. The word preceding
the colon must be followed by one of the bulleted modifiers in order for that code to be
assigned.

Question 18

DConvention.3: Punctuation what does a Point dash .–

indicate, where are they found?

Answer 18

A point-dash is used in both the Tabular List and the Alphabetical Index to indicate there
are fourth character subdivisions.

Question 19

DConvention.3: Punctuation list the uses of Parentheses ( ) in the ICD-10 Classification

Answer 19

Parentheses are used to enclose nonessential modifiers (see DConvention.6: Modifiers).
They are also used to enclose chapters, categories and codes listed in instructional notes,
code ranges in block titles and dagger or asterisk codes in the Tabular List and to enclose
cross-reference terms in the Alphabetical Index.

Question 20

What are the two types of Abbreviations found within ICD-10? What does the abbreviation stand for?

Answer 20

NOS (Not Otherwise Specified)

NEC (Not Elsewhere Classified)

Question 21

What are the meanings

behind the abbreviations described in DConvention.4: Abbreviations?

Answer 21

NOS (Not Otherwise Specified)

Equivalent to ‘unspecified’, i.e. .9. A term without any essential modifier is usually the
unspecified form of the condition. The code assignment is that which directly follows the
lead term in the Alphabetical Index. When the clinician states a diagnosis, problem or
reason for an encounter as a single term which has no modifiers, in classification terms it is
said to be ‘unspecified’ or unqualified or NOS. The coder must ensure there is no further
information in the medical record that would allow for the assignment of a more specific
code.

NEC (Not Elsewhere Classified)

Assignment of a tentative code which uses NEC should be avoided if at all possible. The
category for the term including NEC is to be used only when the coder lacks the
information necessary to code the term to a more specific category. The phrase ‘not
elsewhere classified’ is used in the Tabular List for residual categories to indicate that
other specified variants of the condition may appear in other parts of the classification.
Often, but not always, an exclusion note appears in an ‘NEC’ category, directing the coder
to the code range, category or four character code where the condition is classified.

Question 22

What are the four Relational terms described in DConvention.5: Relational terms?

Answer 22

And

With or with mention of

Without

In, due to and resulting in

Question 23

What does the term ‘And’ mean as described as in DConvention.5: Relational terms?

Answer 23

The use of ‘and’ within code descriptions means and/or. It indicates that the code can be
assigned if either one or both elements within the code description are present.

Question 24

What does the term ‘With or with mention of’ mean as described as in DConvention.5: Relational terms?

Answer 24

‘With’ is used either when two or more conditions combine to form another condition or to
provide additional four character specificity. These terms indicate that both elements in the
code description must be present in the diagnostic statement in order to assign the code.
These terms do not necessarily indicate a cause-effect relationship. ‘With’ always appears
first in the list of modifiers in the Alphabetical Index. (See also DConvention.6: Modifiers)

Question 25

What does the term ‘Without’ mean as described as in DConvention.5: Relational terms?

Answer 25

Indicates that the named element must not be present in the diagnostic statement in order
to assign the code.

Question 26

DConvention.5: Relational terms What do the terms ‘In, due to and resulting in’ indicate?

Answer 26

Indicate a causal relationship between the elements in the title and requires the responsible
consultant to confirm a cause-effect relationship within the medical record before the
code(s) can be assigned. This may be clear from the diagnostic statement or in the
combinations of conditions. In other instances, ICD-10 presumes a relationship unless
otherwise qualified.

These terms are usually used where a condition only occurs because of the presence of
another condition. ‘In’ and ‘due to’ are used interchangeably as they have the same
meaning, and in many cases appear as ‘in (due to)’. In the vast majority of cases, the
subentries have both dagger and asterisk codes. ‘In’ and ‘due to’ are also used in other
situations such as ‘in pregnancy’ or ‘due to drugs’.

Question 27

What are the two types of modifiers in ICD-10?

Answer 27

Nonessential modifiers

Essential modifiers

Question 28

Fully Define DConvention.6: Modifiers

Answer 28

Modifiers are also referred to as qualifiers and are descriptive words used to further
describe or modify a diagnosis. They are found in the Alphabetical Index and the Tabular
List.

Nonessential modifiers

Nonessential modifiers are supplementary words and descriptors which do not affect the
code selection for a given diagnosis. These modifiers may be present or absent in the
diagnostic statement but result in the assignment of the same code.
They appear in parentheses (See also DConvention.3: Punctuation) following the terms
they modify.

Essential modifiers

Essential modifiers are descriptive terms which do affect the code selection for a given
diagnosis. These modifiers describe essential differences (for the purpose of coding) in
site, aetiology, or type of disorder. These terms must appear in the diagnostic statement
for the code to be assigned.

Essential modifiers appear as subterms indented below lead terms. Each indented list is in
alphabetical order, with the following exceptions:
• Whenever the relational term ‘with’ (see also DConvention.5: Relational terms) is
used it is always the first entry of the indented list
• Numbers spelled out into words appear in alphabetical order
• Numbers listed as Arabic numbers appear at the end of the list after all the
modifying words in numeric order
• Numbers listed as Roman numerals appear in numeric order.

Question 29

Which four chapters within ICD-10 have fifth characters mandated for use within the
UK?

Answer 29

Chapter IX Diseases of the circulatory system
Chapter X Diseases of the respiratory system
Chapter XIII Diseases of the musculoskeletal system and connective tissue
Chapter XIX Injury, poisoning and certain other consequences of external causes

Question 30

Why are fifth characters used throughout the ICD-10?

DConvention.7: Fifth characters

Answer 30

Supplementary fifth characters are used in Chapters IX, X, XIII and XIX to add greater
specificity to the codes. Fifth characters activity codes are also available in Chapter XX but
these codes are not to be used for national collection.

Question 31

Which two symbols appear in the Neoplasm Table?

Answer 31

Cross hatch # and diamond