How ICD-11 is organized

Hook

Where do ICD-11 codes live? Not in one flat list. They sit on top of a foundation, and what you code from is built from it.

The foundation component

At the bottom is the Foundation Component. It's a multidimensional collection of every ICD entity: diseases, disorders, injuries, external causes, signs and symptoms. Some entities are broad, like injury of the arm. Others are specific, like laceration of the skin of the thumb. From this one database, WHO builds the tabular list, the index, specialty views, and country versions.

The tabular list you code from

The tabular list is what you code from. In it, entities become categories. Each category has exactly one parent, and categories don't overlap. There are several congruent tabular lists built from the same foundation, one for mortality and morbidity statistics, one for primary care, and specialty versions. In this course, we use the mortality and morbidity statistics list, usually called the MMS.

The chapters

The MMS has 26 numbered chapters, plus a section for functioning assessment and a section for extension codes. Most chapters follow the body systems: the circulatory system, the respiratory system, and so on. A few chapters are special groups, which bring conditions together rather than scattering them by body site: infectious diseases, neoplasms, blood, the immune system, pregnancy and childbirth, the perinatal period, developmental anomalies, and injury. Chapter 25 holds codes for special purposes, and chapter 26 covers traditional medicine conditions.

The rule that decides

One rule matters in practice. If there is any doubt where a condition belongs, the special-groups chapters take priority. That's enforced through the excludes notes at the start of each chapter. So an injury goes to the injury chapter, even if you would have looked for it under a body system.

Recap

Foundation underneath. A tabular list on top. Twenty-six chapters, with the special-groups chapters taking priority when there's doubt. That's the map. Next, we'll learn to read a single code.