# Brief history of ICD



## rahulasrivastava (Feb 25, 2013)

*ICD-10-CM Code Structure*

ICD-10-CM codes can be up to seven digits and are alpha-numeric. 

First three characters of the code describe the “category” example H60 is for otitis externa. First character is always an alphabet from A through Z (except U). Just for remembering – this first character may indicate the chapter to which the code belongs to; like ‘M' for musculoskeletal, example M19 belongs to the chapter ‘diseases of the musculoskeletal system and connective tissue'. Second character is always numeric. Third character is also numeric but could be an alphabet also, example O9A category. 

Fourth, fifth, and sixth characters can be numeric or an alphabet and describes etiology, anatomic site, location, laterality, severity, or other clinical detail. For example, in J02.x category for acute pharyngitis, fourth character describes etiology - ‘0' for streptococcal, ‘8' for other specified organisms and ‘9' for unspecified. In S41.0x category for open wound of shoulder, fifth character describes clinical detail – ‘0' for unspecified open wound, ‘1' for laceration without foreign body, ‘3' for puncture wound without foreign body, etc. In S82.00x category for unspecified fracture of patella, sixth character describes laterality – ‘1' for right patella and ‘2' for left patella. 

Seventh character again can be numeric or an alphabet and describes extension. For example in T33.011x category for superficial frostbite of right ear, seventh character describes extension – ‘A' for initial encounter, ‘D' for subsequent encounter, and ‘S' for sequela. 

If we study the above example of T33.011A superficial frostbite of right ear initial encounter, we can see that all seven characters describing their own story – first character ‘T' for chapter ‘injury' (or T for trauma), second and third character ‘33' for category ‘superficial frostbite', fourth character ‘0' for location ‘head', fifth character ‘1' for anatomic site ‘ear', sixth character ‘1' for laterality ‘right', and seventh character ‘A' for extension ‘initial encounter'.

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