Category and code of ICD-10-WHO

The purpose of the following explanations on categories, class titles and codes as well as on inclusion notes and exclusion notes and other class attributes is to provide an initial understanding of ICD-10-WHO. Encoding requires familiarity with the Instruction Manual (Volume 2).

Category, class title and code

The central element of the Tabular List of ICD-10-WHO is the three-character category or three-character code. A category is defined by its class title and an alphanumeric code. The first character denotes the letter of the chapter. In case of the three-character category the code is marked as highlighted in black.

The term "code" is often used synonymously with "category".

Some of the three-digit categories, such as "A38 Scharlach" (Scarlet fever) represent individual pathological conditions; however, in general, one three-character category comprises several diseases with similar characteristics, for example: D 27 refers to benign ovarian neoplasms. On this level, "and" in the class title stands for and/or, square brackets contain synonyms and round brackets optional additions.

The descriptions included in a particular category of the Tabular List are not final; they serve as examples for the content of that category and as an indication of its scope and delimitation. To that end, preferred terms are used. By contrast, in addition to these preferred terms, the associated Alphabetical Index also contains many other currently used diagnostic terms, including synonyms.

Very few categories have a structure as simple as that of D27. Code and class title can be supplemented with subcategories and class attributes.

Three- and four-character categories

Almost all categories have four-character subcategories. The fourth digits are separated from the three-digit code by a decimal point. Their values can range between 0 and 9, but not all values have to be used. Subcategories ending in 8 or 9 are mostly used for "sonstige" (other specified, 8) and "sonstige nicht näher bezeichnete" (other non-specified, 9) pathological states within this category. Codes without subcategories are referred to as terminal codes. The basic rule is to encode as specifically as possible, i.e. to use subcategories if available within a category. However, only three-character codes are mandatory for reporting on an international level. In addition to chapter and block titles, the ICD-10-WHO List of three-character categories ("Dreistellige allgemeine Systematik DAS") contains all three-character codes without subcategories or reference notes.

Postcoordinated codes of ICD-10-WHO

Five-character subcategories are found in Chapters XIII, XIX and XX. They are not explicitly included as five-character codes in the print and HTML version of the Tabular List, but have to be assembled by the encoder on the basis of encoding notes and a subclassification list of possible values for the fifth digit. In the following example, the four-character code of the S72 category is complemented with 1 in fifth place to indicate an open ("offen") fracture ; if the fracture was closed ("geschlossen") or no specific information available, the fourth digit would be 0. "Fracture of lower end of femur, open" is thus encoded as S72.41: "Distale Fraktur des Femurs, offen".

Codes generated in this manner are referred to as postcoordinated codes. A subclassification referring to an entire chapter or a whole block of categories is placed to preface the chapter or block. This is the case for example in the preface to Chapter XIII, i.e. the list on the site of musculoskeletal involvement.

Dagger and asterisk codes in the "dagger and asterisk" system

Most codes do not contain any special characters other than the decimal point where applicable. However, there are two special kinds of codes, indicated with a dagger or an asterisk.

Normally, ICD classifies each pathological condition under a single aspect, i.e. each condition is allocated exactly one code. The "dagger and asterisk" system permits the classification of a disease under two different aspects, i.e. according to its aetiology and its manifestation. The disease is then assigned a combination of a dagger code for aetiology and an asterisk code for manifestation: A17.9+ G99.8*. The Instruction Manual contains further details and examples for the "dagger and asterisk" system.

Dagger codes: Primary codes

Dagger codes classify according to aetiology. Dagger codes are primary codes; this means that they can be but do not have to be combined with an asterisk code. Frequently, the dagger code is supplemented with the optional asterisk code. Apart from codes marked as dagger codes, each random primary code can be used as an aetiology code and combined with an asterisk code. In this case, the aetiology code is marked with a dagger by the encoder.

Asterisk codes: Additional codes

Asterisk codes designate the manifestation of a disease. As additional codes, they must never be used on their own but only as part of a dual encoding in the "dagger and asterisk" system, i.e. always in conjunction with a dagger code or another primary code. Very often, the corresponding dagger code is given for an asterisk code.

Class attributes: definitions, inclusion notes, exclusion notes and others

Chapters, blocks and categories often include a range of clarifying comments. If such class attributes follow a chapter title, they apply to all categories within the chapter, if they follow a block title, they apply to all categories within the block, if they follow a category title, they apply to the category and all of its subcategories.


Occasionally - particularly in Chapter V - definitions are provided immediately underneath the class title for the clinical characteristics referred to in the class title.

Inclusion and exclusion notes

Inclusions and exclusions indicate which diseases fall into a certain category and which do not. Inclusion terms are often but not always indicated by "Inkl." (for inclusive) preceding the name of the disease. Exclusion terms can always be identified by a preceding "Exkl." (for exclusive). For diseases mentioned under exclusions, the code of the applicable category is given in round brackets.

As for class titles, for inclusion notes, too, additional optional terms can be provided in round brackets. In the following example I10, the inclusion diagnosis of "Hypertonie" (hypertension) always falls into the I10 category, completely irrespective of whether the term "Hypertonie" is specified by one or more of the expressions included in brackets.

For inclusion notes and exclusion notes, lists can be included for a particular term, as e.g. for I10 or I24.0; the term as list heading is separated from the list by a colon. The list heading can be the name of a disease or an incomplete sentence as in I10, but also a single adjective such as "akut" ("acute") or part of a composite expression such as "Koronar" ("coronary"). The lists contain possible additions to the list heading; the condition thus described only falls into this category if it is complemented by at least one of the attributes specified in the list.

Frequently, these lists take the form of two-column tables: a number of terms in column 1 (separated by a vertical line or a brace in older versions) are juxtaposed to one or more terms in column 2. Each term in column 1 has to appear together with at least one term from column 2 for the condition thus described to fall into that particular category. Correct disease descriptions falling into subcategory I24.0 include "Embolie der Koronararterien ohne nachfolgenden Myokardinfarkt" (Embolism of the coronary arteries not resulting in myocardial infarction) or "Koronarverschluss ohne nachfolgenden Myokardinfarkt" (Coronary occlusion not resulting in myocardial infarction). Terms in round brackets in the list title are optional; however, the descriptive term must include at least one expression from each column in addition to "coronary" for the condition thus described to fall into this category.

Notes and encoding hints

Notes indicated by a preceding "Hinw.:" ("Hinweis") contain further information.

Encoding hints indicate, for example, whether additional codes have to be used or a subclassification applied.

Point-dash notation and other formal conventions

Point-dash notation: For codes mentioned under exclusion notes, three-character codes that are differentiated by subcategories are shown in the point-dash notation, i.e. as (B69.-) rather than (B69). This indicates to the encoder that the category comprises subcategories and that the appropriate code for the specific case may be found there.

Square brackets after class titles and inclusion terms contain synonymous descriptions, round brackets after class titles as well as after inclusion and exclusion notes include optional description elements.

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