This section is a quick reference to the basics of ICD-10-CM code types and structure. It includes a description of the two basic types of ICD-10-CM codes, a table illustrating diagnosis codes in ICD-10-CM that convey external cause (mechanism/intent) information, a description of the structure of ICD-10-CM codes, and two tables illustrating the key differences between ICD-9-CM and ICD-10-CM injury diagnosis codes and external cause of injury codes.

 

Types of ICD-10-CM codes

There are two basic types of ICD-10-CM codes used for injury and drug overdose surveillance:

1. Diagnosis codes (“S” and “T” codes), which contain information about the body region and nature of injury – for example left leg fracture or scalp laceration
2. External cause of injury codes (“V,” “W,” “X” and “Y” codes, and some T codes) which answer the following questions about the circumstances of the injury:
   • How did it occur? What was the mechanism or cause of the injury?
   • What was the intent? Unintentional, intentional self-harm, assault, or undetermined
   • Where did it occur? Place of occurrence codes (Y92)
   • What the person was doing at the time the injury occurred? Activity codes (Y93)
   • What was the person’s status at the time of injury? Status codes (Y99) Civilian, military, volunteer, or other

 

This toolkit focuses on ICD-10-CM diagnosis codes as well as external cause of injury codes that convey mechanism and intent information - referred to throughout this toolkit as “external cause of injury codes”. Place of occurrence, activity, and status external cause of injury codes may be useful to injury researchers and epidemiologists but are not explored in this toolkit.

 

Diagnosis codes and external cause of injury codes complement each other to give a rounded picture of an injury or overdose. External cause of injury codes are useful from a public health perspective because they shed some light on how and why an injury occurred and hence how it might have been prevented. On the contrary, diagnosis codes have more utility from a health service delivery perspective and inform reimbursement.  Per the ICD-10-CM Official Guidelines for Coding and Reporting: “Unless a provider is subject to a state-based external cause of injury code reporting mandate or these codes are required by a particular payer, reporting of ICD-10-CM codes in Chapter 20, External Causes of Morbidity, is not required.” Thus, while medical coders are required to submit diagnosis codes for reimbursement purposes, the percentage of records that have both an injury diagnosis code and an external cause of injury code can vary by jurisdiction and facility. Epidemiologists should determine the rate of external cause coding within their dataset prior to interpreting the data.

It is important to note that in ICD-10-CM, a handful of “T” codes actually function as both a diagnosis and external cause of injury code. This applies to overdose codes (T36-T50) and toxic effects codes (T51-T65), where information about the drug or substance involved and the intent are captured a single code. There are several other “T” diagnosis codes that also contain external cause information. See table below.

 

Diagnosis codes in ICD-10-CM that convey external cause (mechanism/intent) information

 

ICD-10-CM Diagnosis code (T code)	Type of External Cause
T14.91	Suicide attempt
T15-T19	Effects of foreign body entering through natural orifice
T36-T50 with a 6th character of 1, 2, 3, or 4 (Exceptions: T36.9, T37.9, T39.9, T41.4, T42.7, T43.9, T45.9, T47.9, and T49.9 with a 5th character of 1, 2, 3, or 4)	Poisoning by drugs, medicaments, and biological substances
T51-T65	Toxic effects of substances chiefly non-medicinal as to source
T71	Asphyxiation
T73	Effects of deprivation
T74, T76	Adult and child abuse, neglect, and other maltreatment, confirmed or suspected
T75.0, T75.1, T75.2, T75.3	Effects of lightning, unspecified effects of drowning, effects of vibration, motion sickness

 

Structure of ICD-10-CM codes

Both diagnosis and external cause of injury codes in the ICD-10-CM code set can have three to seven alphanumeric characters. The first character is always alpha, the second character is always numeric, and characters 3-7 are alpha or numeric. The first three characters of an ICD-10-CM code designate the general category in which the code belongs, which is further expanded in the fourth, fifth, and sixth characters to add more specific details on related etiology (mechanism and/or intent), anatomic site, and severity. For codes related to injury and overdose, the 7^th character denotes the encounter type (e.g., initial encounter, subsequent encounter, or sequelae). The character for encounter type must always be in the 7^th position, so if a code has less than 6 characters and requires a 7^th character extension, all of the empty character spaces should be filled with the placeholder “X”. A decimal is placed between the 3^rd and 4^th characters, however these decimals may be removed during the data cleaning and preparation stage.

 

Key Differences Between ICD-9-CM and ICD-10-CM³

 

Injury Diagnosis Codes
ICD-9-CM	ICD-10-CM
2,600 codes	43,000 codes
Code range 800-995	“S” and “T” codes
Codes consist of 3-5 characters	Codes consist of 3-7 characters; some codes have an “X” placeholder character to accommodate new codes in the future
Primary axis is nature of injury	Primary axis is body region
No character to indicate laterality	Characters within the code indicate left, right, bilateral, unspecified laterality
Limited detail on type of fracture	Detailed information on type of fracture
Laceration codes do not specify presence/absence of a foreign body	Laceration codes specify presence/absence of a foreign body
Limited information on superficial injuries	Detailed information on superficial injuries
Codes for poisoning and adverse effects of drugs	Codes for poisoning, adverse effects and underdosing of drugs
Poisoning: coded using both diagnosis codes and external cause of injury codes	Poisoning: coded using a diagnosis code only (T code); a character in the code identifies the intent of the poisoning (unintentional, intentional self-harm, assault, or undetermined)
Asphyxiation: 994.7	40 diagnosis codes for asphyxiation or strangulation by different mechanisms and intents
No distinction between suspected and confirmed child/adult abuse	New codes to distinguish between suspected and confirmed child/adult abuse
No distinction between initial and subsequent encounter for care	Most codes have a 7th character to distinguish between initial and subsequent encounter for care
Limited late effect codes	Most codes have a 7th character indicating sequelae (late effects)

 

 

External Cause of Injury Codes
ICD-9-CM	ICD-10-CM
1,300 codes	7,500 codes
External cause of injury codes begin with “E” and are commonly referred to as “E-codes”	External cause of injury codes begin with “V,” “W,” “X” or “Y”
Codes contains 3-5 characters	Code contains 3-7 characters; some codes have an “X” placeholder character to accommodate new codes in the future
No distinction between initial or subsequent encounters	7th character to designate initial or subsequent encounter
Limited external cause of injury codes for late effect	7th character indicates sequelae (late effects)
External cause of injury codes for intentional self-inflicted injuries are referred to as Suicide/self-inflicted	External cause of injury codes for intentional self-inflicted injuries are referred to as Intentional self-harm
External cause of injury codes for intentional harm by other persons are referred to as Homicide and injury purposely inflicted by other persons	External cause of injury codes for intentional harm by other persons are referred to as Assault
Includes specific external cause of injury codes for: poisoning and toxic effects of substances, asphyxiation, effects of foreign bodies, deprivation and neglect, lightning, and vibration.	Includes specific diagnosis (nature of injury) codes for: poisoning and toxic effects of substances, asphyxiation, effects of foreign bodies, deprivation and neglect, lightning, and vibration.
Includes external cause of injury codes for perpetrator of child and adult abuse (E967.0-.9); includes diagnosis codes for child maltreatment and abuse (995.50-995.59) and adult maltreatment and abuse (995.80-.85)	External cause of injury codes for perpetrator of assault, maltreatment and neglect (Y07) are expanded; includes diagnosis codes to specify adult and child abuse, neglect, and other maltreatment, confirmed (T74) and suspected (T76)