Why is a unified classification needed?
Medical nomenclature (agreed-upon names of diseases) and classification are constantly evolving. The emergence of previously unknown pathologies and deeper understanding of etiology and pathogenesis require regular data updates. This is handled by the WHO expert committee, which periodically holds assemblies and relies on statistics from UN member states. The compilation of an updated version of the document is called revision.
Transitioning to a unified standard is strictly mandatory for all medical institutions. Even if a specific country has historically established its own traditions for making a diagnosis, a physician is required to adapt it to the international format. Global unification solves several crucial tasks at once:
- Collecting accurate global statistics on morbidity and mortality.
- Tracking trends in human health changes.
- Organizing humanitarian and specialized aid to countries.
- Developing preventive measures at the regional and continental levels.
- Training qualified medical personnel.
Document structure
The official edition (using the widely used ICD-10 from 1993 as an example) has been translated into UN official languages and consists of three volumes:
- Volume 1 — a special list of categories intended for statistical compilation.
- Volume 2 — a compendium of detailed instructions and rules for using the system.
- Volume 3 — the alphabetical index of diseases and injuries. It allows searching by keywords for diseases, syndromes, as well as external circumstances of injuries (e.g., a fall or a fire) and lists of chemical substances or biological agents that caused poisoning or an adverse reaction.
How the coding system works
The ICD is based on a convenient alphanumeric code. 25 letters of the Latin alphabet are used to designate categories. Up to one hundred three-character categories are assigned to each letter.
If diagnosis refinement is required, a four-character code is used: a decimal point is placed after the first three characters, followed by an additional digit. In narrow medical specialties such as psychiatry, dentistry, or oncology, the detailing can be even deeper—introducing fifth and sixth digits for this purpose. Furthermore, the duration of the disease is mandatory in coding: whether the process is acute or has become chronic.
Principles of disease grouping
The entire diversity of pathologies (over 30,000) is distributed across 21 chapters. The main principle for forming chapters is nosological, relying on etiology, pathogenesis, and outcomes. However, this is not always applicable, so other approaches are also used:
- The nosological principle in its pure form is represented in Chapter I (A00–B99) "Certain infectious and parasitic diseases". In Chapter II (C00–D48) "Neoplasms", it works only partially, as the etiology of tumors is not fully understood, although risk factors and pathogenesis are known.
- The organ-group (anatomic) principle groups pathologies by organ systems. Diseases of the blood (Chapter III, D50–D89), respiratory system (Chapter X, J00–J99), digestive system (Chapter XI, K00–K93), and genitourinary system (Chapter XIV, N00–N99) are grouped this way.
- Syndrome-based classification is used when the cause and mechanism of development of a condition are unknown. This includes various clinical and laboratory symptoms (Chapter XVIII, R00–R99).
- Health factors are separated into a distinct Chapter XXI (Z00–Z99). These are situations when a person visits a facility not due to an illness, but, for example, for vaccination or a routine check-up.
Briefly: answers to topical questions
Which ICD-10 disease chapters are grouped according to the organ-group (anatomic) principle?
According to the organ-group (anatomic) principle, ICD-10 groups diseases of individual organ systems. These chapters include:
- Chapter III (D50–D89) — Diseases of the blood and blood-forming organs.
- Chapter X (J00–J99) — Diseases of the respiratory system.
- Chapter XI (K00–K93) — Diseases of the digestive system.
- Chapter XIV (N00–N99) — Diseases of the genitourinary system.
In which ICD-10 chapters are injuries, poisonings, and their external causes coded?
Injuries, poisonings, and the consequences of external causes in ICD-10 belong to the chapter on injury and external causes. The exact chapter number is not specified in the sources.
For external causes of injuries, Volume 3 of ICD-10 provides a separate index of external causes of injuries, taking into account the circumstances of their occurrence, such as a fire or a fall. Volume 3 also contains a list of medicinal, biological substances, and chemicals used for poisonings and adverse reactions.
What additional codes are used in ICD-10 to indicate the histological structure of neoplasms?
To indicate the histological structure of neoplasms, morphological codes of the International Classification of Diseases for Oncology (ICD-O or ICD-O) are used. These codes are utilized to detail the morphological diagnosis (e.g., in neuroendocrine, non-epithelial tumors, and carcinomas). In addition, dentistry uses a specialized ICD-DA classification, which includes important supplements:
- Appendix 1 — histological types of odontogenic tumors.
- Appendix 2 — histological types of salivary gland tumors.
What conditions and reasons for contact are included in Chapter XXI "Factors influencing health status and contact with health services" (Z00–Z99)?
Chapter XXI "Factors influencing health status and contact with health services" (Z00–Z99) includes various factors that affect a person's health status, as well as reasons for patient visits to medical institutions. Such reasons include:
- Preventive examinations — conducting routine medical check-ups.
- Vaccination — administration of prophylactic immunizations.
To remember the structure of ICD volumes, use the mnemonic "SIU": Statistics (Volume 1), Instructions (Volume 2), Index (Volume 3).
Class and exam questions
Who is responsible for revising and updating the ICD?
This work is carried out by a committee of experts from the World Health Organization (WHO). They periodically convene assemblies and analyze data from UN member states to incorporate new medical knowledge.
Is it permissible to use national disease names instead of ICD codes?
No, the use of ICD is strictly mandatory for all medical professionals. Any diagnosis must comply with the international classification, even if it contradicts local traditions.
How are injuries and poisonings coded?
Special sections in the alphabetical index (Volume 3) are provided for them. They account for external circumstances (e.g., fire) and specific drugs or chemicals that caused the reaction.
What to do if the etiology and pathogenesis of the disease are unknown?
Such conditions are classified by the syndromic principle. A separate chapter is allocated for them, including symptoms, signs, and abnormal clinical and laboratory findings not elsewhere classified.
What else to study on this topic
- Features of coding acute and chronic conditions
- Detailing diagnoses using the fifth and sixth digits in narrow specialties
- Classification of external causes of injuries and iatrogenesis
- Factors influencing health status and contact with health services (Chapter XXI)
- Differences between medical nomenclature and classification
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