Anatomy of a code

Hook

5A11. Looks like a jumble. But every character is there for a reason, and once you know the rules, you can read any ICD-11 code.

The first character

The first character tells you the chapter. It can be a number or a letter. 1A00 is a code in chapter 1. BA00 is a code in chapter 11. A letter A in the first position means chapter 10. And a code that starts with X is not a diagnosis at all: it's an extension code.

The pattern

The second position is always a letter. That's what sets ICD-11 codes apart from ICD-10, where the second character is a number. The third is a digit. And the letters O and I are never used, so they can't be confused with zero and one.

Reading a real code

Take 5A11. The five tells you it's in chapter five, endocrine, nutritional or metabolic diseases. The whole code is Type 2 diabetes mellitus. Read the characters as an address: chapter first, then narrowing down to the category.

The last letter

Watch the last character. A Y is reserved for "other specified", and a Z for "unspecified". The difference matters. Choose unspecified when the information isn't in the documentation. Choose other when the documentation is specific, but the classification has no category for it, so you pick the closest match. For example, DA63.Z is duodenal ulcer, unspecified. A few chapters that are very large also use F and G for these residual categories.

What can stand alone

A stem code can be used on its own. Blocks, the groupings above codes, have no codes and are never used for coding. Extension codes can never be used without a stem code.

Recap

First character, the chapter. Second, a letter; third, a digit. No O, no I. A Y or a Z at the end means a residual category. That's how you read a code.