ICD-10 Explained

What is ICD-10?

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ICD-10 diagnosis codes have between 3 and 7 characters. ICD-10 structure

Codes with three characters are included in ICD-10-CM as the heading of a category of codes that may be further subdivided by the use of any or all of the 4th, 5th and 6th characters. Digits 4-6 provide greater detail of etiology, anatomical site, and severity. A code using only the first three digits is to be used only if it is not further subdivided.

A code is invalid if it has not been coded to the full number of characters required. This does not mean that all ICD-10 codes must have 7 characters. The 7th character is only used in certain chapters to provide data about the characteristic of the encounter.

Examples of where the 7th character can be used include injuries and fractures, as illustrated in the following tables:


Injuries and External Causes


Value Description Value Description
A Initial encounter A Initial encounter for closed fracture
D Subsequent encounter B Initial encounter for open fracture
S Sequela D Subsequent encounter for fracture with routine healing
G Subsequent encounter for fracture with delayed healing
K Subsequent encounter for fracture with nonunion
P Subsequent encounter for fracture with malunion
S Sequela

A dummy placeholder of “X” is used with certain codes to allow for future expansion and/or to fill out empty characters when a code contains fewer than 6 characters and a 7th character applies. When a placeholder character applies, it must be used in order for the code to be considered valid.

Below are specific examples of ICD-10 diagnosis codes. The use of combination codes, increased specificity, and the “X” placeholder is illustrated:


Combination Codes
I25.110 Atherosclerotic heart disease of native coronary artery with unstable angina pectoris
Increased Specificity
S72.044G Non-displaced fracture of base of neck of right femur, subsequent encounter for closed fracture with delayed healing
C50.511 Malignant neoplasm of lower-outer quadrant of right female breast
C50.512 Malignant neoplasm of lower-outer quadrant of left female breast
“X” Placeholder
H40.11X2 Primary open-angle glaucoma, moderate stage

To prepare for the upcoming transition, PGM Billing developed an ICD-10 code conversion tool that allows users to convert ICD-9 to ICD-10 codes and vice versa by selecting the ICD conversion type followed by a user defined code.