A Guide to Understanding: What are the classification of clinical diseases?

October 1, 2025 •

4 min read

According to the World Health Organization (WHO), the International Classification of Diseases (ICD) has served as the global standard for decades, enabling health professionals to track and compare health data worldwide. Understanding what are the classification of clinical diseases is vital not only for this statistical reporting but also for diagnosis, treatment planning, and public health management.

Quick Summary

Clinical diseases are categorized using several distinct methods, such as by cause (etiology), affected body part, disease process, and duration. A key international standard is the ICD system, used for global health statistics and documentation.

Key Points

International Standard: The World Health Organization (WHO) maintains the International Classification of Diseases (ICD), the global system for coding and tracking health conditions for morbidity and mortality statistics.
Categorization by Cause: Etiological classification groups diseases by their origin, distinguishing between extrinsic (external), intrinsic (internal), and idiopathic (unknown) causes.
Grouping by Body System: Anatomic or topographic classification organizes diseases based on the specific organ or system they primarily affect, which aligns with medical specializations.
Understanding Disease Process: Pathophysiological classification focuses on the functional and structural mechanisms of the disease, such as neoplastic (cancers) or inflammatory processes.
Temporal Distinction: Diseases are also classified by their duration as either acute (sudden and short-lived) or chronic (long-lasting and slow-developing).
Communicability Factors: Classifying diseases as communicable (transmissible) or non-communicable (non-transmissible) is vital for public health strategies and infection control.

The Global Standard: International Classification of Diseases (ICD)

The most prominent and internationally recognized system for classifying diseases is the International Classification of Diseases (ICD), published by the World Health Organization (WHO). The latest version, ICD-11, came into effect in January 2022, representing a major step forward for global health data. The primary purpose of the ICD is to provide a common language for systematic recording, analysis, and comparison of mortality (causes of death) and morbidity (illness) data across different countries and time periods.

Unlike traditional classifications, which may focus on a single aspect, the ICD is comprehensive. It assigns alphanumeric codes to a wide range of health-related conditions, symptoms, and external causes of injury. These codes are critical for healthcare recording, billing, research, and public health policy development. The digital-first nature of ICD-11, with its vast database of over 55,000 unique codes, allows for greater specificity and detail in clinical documentation.

Classification by Cause (Etiology)

One of the most logical and useful ways to classify diseases is by their cause, or etiology. Knowing the cause of a disease is fundamental to prevention and effective treatment. Etiological classifications group conditions based on what triggers them. Diseases can have intrinsic, extrinsic, or idiopathic etiologies.

Extrinsic Etiology: Caused by external factors. This includes infectious diseases caused by pathogens like bacteria, viruses, and fungi. Other extrinsic causes are environmental, such as exposure to radiation or toxic chemicals.
Intrinsic Etiology: Originates from internal dysfunctions within the body. Examples include genetic or inherited conditions (like hemophilia), metabolic disorders (such as diabetes), or issues with the immune system (like autoimmune diseases).
Idiopathic Etiology: Diseases where the underlying cause is currently unknown. Many diseases were once idiopathic before medical research identified their root cause. For example, hypertension (high blood pressure) is often classified as essential (idiopathic) when no cause is identified.

Classification by Affected Body System

Medical practice often organizes and specializes based on body systems, so classifying diseases by the organ or system they affect is a common approach. This is sometimes referred to as anatomic or topographic classification and forms the basis for many medical specialties.

Cardiovascular System: Diseases affecting the heart and blood vessels, such as coronary artery disease or hypertension.
Respiratory System: Conditions affecting the lungs and airways, like asthma or pneumonia.
Digestive System: Disorders of the stomach, intestines, liver, and other digestive organs, such as Crohn's disease or gastritis.
Nervous System: Diseases of the brain, spinal cord, and nerves, including conditions like multiple sclerosis or epilepsy.
Endocrine System: Disorders of the body's hormones, such as diabetes mellitus.

Pathophysiological Classification

This method categorizes diseases based on the underlying functional changes or disease processes, regardless of the organ system. It focuses on how a disease causes its effects on the body. Examples of pathophysiological classifications include:

Neoplastic Diseases: Involving uncontrolled cell growth, covering all types of cancer, regardless of their location.
Inflammatory Diseases: Characterized by inflammation, which can be part of many different conditions, such as arthritis.
Degenerative Diseases: Involving the gradual deterioration of cells and tissue function, such as osteoarthritis.

Acute vs. Chronic Classification

Diseases can also be classified based on the duration of their symptoms and progression. This is a simple but important distinction for treatment and prognosis.

Acute Diseases: These have a sudden onset, short duration, and often resolve completely. Examples include the common cold or a sprained ankle.
Chronic Diseases: These persist for a long period, often more than three months, and may require ongoing management. They typically develop slowly. Heart disease, diabetes, and asthma are examples of chronic conditions.

Communicable vs. Non-communicable Classification

Another fundamental way to classify diseases is by whether they can be transmitted from one person or species to another.

Communicable (Infectious) Diseases: Caused by specific biological agents and spread from an infected source to a susceptible host. This includes contagious diseases like influenza and communicable diseases like sexually transmitted infections.
Non-communicable Diseases (NCDs): These are non-transmissible and include a wide range of chronic conditions such as heart disease, cancer, and diabetes.


Classification Basis	Description	Examples
Etiology	Based on the cause of the disease.	Infectious (viral, bacterial) or Genetic (hemophilia).
Anatomic/Topographic	Based on the organ or body system affected.	Heart disease (cardiovascular) or Arthritis (musculoskeletal).
Pathophysiology	Based on the underlying functional or structural changes.	Neoplastic (cancer) or Inflammatory (rheumatoid arthritis).
Duration	Based on the length of the disease's course.	Acute (common cold) or Chronic (diabetes).
Communicability	Based on whether the disease is transmissible.	Communicable (influenza) or Non-communicable (cancer).
International Standard (ICD)	Comprehensive system for coding and tracking health information.	Uses alphanumeric codes for statistical reporting.

Conclusion

The diverse classification systems for clinical diseases are not mutually exclusive but rather provide different lenses through which to understand and manage health conditions. The International Classification of Diseases (ICD) offers a universal framework essential for global health surveillance and consistent record-keeping. However, other classifications based on etiology, anatomy, pathophysiology, and temporality remain critical for clinical practice and research. Each system serves a specific purpose, from guiding diagnostic approaches to informing public health interventions, underscoring the complexity and multi-faceted nature of understanding and addressing human illness.

For more in-depth information, the World Health Organization's website on the International Classification of Diseases offers comprehensive resources(https://www.who.int/standards/classifications/classification-of-diseases).

Frequently Asked Questions

The ICD, or International Classification of Diseases, is a global standard for recording and reporting health information and causes of death. Published by the WHO, it uses a system of alphanumeric codes to categorize diseases, injuries, and other health conditions.

Diseases can be classified in multiple ways, including by their cause (etiology), the body system they affect, their underlying disease process (pathophysiology), their duration (acute or chronic), and their transmissibility (communicable or non-communicable).

Etiological classification categorizes diseases based on their cause, such as internal factors like genetics (intrinsic etiology), external factors like pathogens or toxins (extrinsic etiology), or when the cause is unknown (idiopathic).

Acute diseases have a sudden onset and are of short duration, often resolving completely, like the common cold. Chronic diseases, conversely, develop slowly and persist over a long period, often requiring ongoing management, such as diabetes or heart disease.

An idiopathic disease is a condition whose cause is currently unknown or has not yet been identified by medical science.

This classification method, also known as anatomic or topographic, groups diseases based on which major organ or body system they affect, such as cardiovascular diseases, respiratory diseases, or diseases of the nervous system.

Classifying diseases is crucial for several reasons: it provides a standardized way to diagnose and describe conditions, enables global health statistics and research, helps track public health trends, and guides appropriate treatment and management strategies.