External causes of morbidity
This chapter does not describe injuries themselves — it explains how injuries or health conditions happened. These codes are always used in conjunction with codes from the Injury chapter (S00-T88). Think of them as contextual metadata for trauma and poisoning events.
The chapter is organized by mechanism and intent. It includes transport accidents (motor vehicle, pedestrian, cyclist), falls (from stairs, ladders, same level), exposure to mechanical forces, drowning, suffocation, burns due to fire or hot substances, firearm discharge, assault, self-harm, and exposure to environmental factors such as extreme temperatures or natural disasters.
Intent is a critical element: accidental, intentional self-harm, assault, legal intervention, or undetermined. Some codes also specify the place of occurrence (home, school, workplace), activity at the time of injury (sports, leisure, work), and external status (civilian, military). While these codes may not always affect reimbursement directly, they are vital for injury surveillance, prevention programs, occupational health research, and public health policy. They allow health systems to track patterns and identify risk factors at a population level.
Clinical & Coding Guidelines
Chapter Notes
- This chapter permits the classification of environmental events and circumstances as the cause of injury, and other adverse effects. Where a code from this section is applicable, it is intended that it shall be used secondary to a code from another chapter of the Classification indicating the nature of the condition. Most often, the condition will be classifiable to Chapter 19, Injury, poisoning and certain other consequences of external causes (S00-T88). Other conditions that may be stated to be due to external causes are classified in Chapters I to XVIII. For these conditions, codes from Chapter 20 should be used to provide additional information as to the cause of the condition.