Format and Structure:

The ICD-10-CM Tabular List contains categories, subcategories and codes. Characters for categories, subcategories and codes may be either a letter or a number. All categories are 3 characters.

A three-character category that has no further subdivision is equivalent to a code. Subcategories are either 4 or 5 characters. Codes may be 3, 4, 5, 6 or 7 characters.

That is, each level of subdivision after a category is a subcategory. The final level of subdivision is a code. Codes that have applicable 7th characters are still referred to as codes, not subcategories.

A code that has an applicable 7th character is considered invalid without the 7th character. The ICD-10-CM uses an indented format for ease in reference.