Structure of an ICD-10-CM Code

Letter	Number or Letter
1st Digit	2nd Digit	3rd Digit		4th Digit	5th Digit	6th Digit	7th Digit
C	5	0	.	5	1	2*
Category				Etiology, anatomic site, severity, laterality			Added code extensions for obstetric, injuries and external causes of injury

* C50.512: Malignant neoplasm of lower-outer quadrant of left female breast

Length	3-7 digits
Character 1	Letter only (all letters except U are used)
Character 2	Number only
Characters 3-7	Numbers or letter
Decimal	After 3rd character (not counted)
Placeholder	Use of “x” as a dummy placeholder
Letter Format	Letters are case-sensitive

Updated: December 3, 2018