What’s Different About ICD-10?

The following is the second in a series of articles on the transition from ICD-9 to ICD-10. The AGA will continue to provide updates as they are released by CMS.

What are the structural differences between ICD-9-CM and ICD-10-CM?


  • Has three to five digits.
  • In chapters one to 17, all characters are numeric.
  • In supplemental chapters, the first digit is alpha (E or V); the remainder are numeric.



  • 496 Chronic airway obstruction not elsewhere classified (NEC).
  • 511.9 Unspecified pleural effusion.
  • V02.61 Hepatitis B carrier.


  • Has three to seven digits.
  • Digit one is alpha (A-Z, not case sensitive).
  • Digit two is numeric.
  • Digit three is alpha (not case sensitive) or numeric.
  • Digits four to seven are alpha (not case sensitive) or numeric.



  • A66 Yaws.
  • A69.20 Lyme disease, unspecified.
  • O9A.311 Physical abuse complicating pregnancy, first trimester.
  • S42.001A Fracture of unspecified part of right clavicle, initial encounter for closed fracture.


ICD-10-CM files, information and mapping between ICD-10-CM and ICD-9-CM can be found on the CDC Web site. ICD-10-CM files, information and general equivalence mappings between ICD-10-CM and ICD-9-CM can be found online. Read CMS information about ICD-10.

In addition, on Nov. 17 from 12:30-2:30 p.m. ET, CMS will host a national provider call that will provide an overview of ICD-10-CM and how it differs from ICD-9-CM. The presentations will include the major impacts providers should consider when planning to update any systems with ICD-10 codes. Issues such as differences in code length, alpha-numeric characters and increased details captured by the codes will be explained. View information about registering for the call.