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Coding for External Causes of Morbidity in ICD-10-CM

By Lauri Gray, CPC, RHIT
July 03, 2012

Codes for external causes of morbidity provide a framework for systematically collecting patient health related information on the external cause of death, injury, poisoning and adverse effects. These codes define the manner of the death or injury, the mechanism, the place of occurrence of the event, the activity, and the status of the person at the time death or injury occurred. Manner refers to whether the cause of death or injury was unintentional/accidental, self-inflicted, assault, or undetermined. Mechanism describes how the injury occurred such as a motor vehicle accident, fall, contact with a sharp object or power tool, or being caught between moving objects. Place identifies where the injury occurred, such as a personal residence, playground, street, or place of employment. Activity indicates the activity of the person at the time the injury occurred such as swimming, running, bathing or cooking. External cause status is used to indicate the work or non-work status of the person at the time death or injury occurred such as work done for pay, military activity, volunteer activity, or leisure activity. 

In ICD-10-CM, codes for external causes of morbidity (V00-Y99) are found in Chapter 20. External cause codes classify environmental events and other circumstances as the cause of injury and other adverse effects. Codes in this chapter are always reported as a secondary code with the nature of the condition or injury reported as the first-listed diagnosis. Examples of the nature of a condition or injury include fracture, laceration, abrasion, or traumatic intracerebral hemorrhage. The nature of an injury or other consequence of an external cause is reported with codes in Chapter 19, Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88). Conditions other than injuries may also result from an external cause such as a myocardial infarction precipitated by strenuous activity such as shoveling snow. In this case the nature of the condition is the myocardial infarction reported with codes from categories I21-I22 and external cause codes would be reported additionally to identify the activity, place and external cause status.

While not all third party payers require reporting of external cause codes, they are a valuable source of information to public health departments and other state agencies regarding the causes of death, injury, poisoning and adverse effects. In fact, more than half of all states have mandated that hospitals collect external cause data using statewide hospital discharge data systems. Another third of all states routinely collect external cause data even though it is not mandated. There are also 15 states that have mandated statewide hospital emergency department data systems requiring collection of external cause data.

Alphabetic Index to External Causes

There is a separate alphabetic index for external causes in ICD-10-CM. It follows the Table of Drugs and Chemicals in both coding systems. Unfortunately, the alphabetic index for external causes in ICD-10-CM continues to be as difficult to navigate as the one in ICD-9-CM. This means that once an external cause code is identified in the index, the tabular must be carefully reviewed to ensure that the code identified is the correct code. All includes and excludes notes and any additional instructions must be reviewed. After reviewing the tabular it may be necessary to return to the external cause alphabetic index and search again under different terms to ensure that the correct external cause code has been located.

7th Character Extensions

Codes that describe the manner and mechanism of injury require 7th character extensions. The 7th characters used in for external cause codes are the same as those used for the majority of codes in Chapter 19 Injury, Poisoning and Certain Other Consequences of  External Causes and the characters have the same definitions. The 7th character extensions for Chapter 20 and their definitions are as follows:

A          Initial encounter. Initial encounter is defined as the period when the patient is receiving active treatment for the injury, poisoning, or other consequences of an external cause. An ‘A’ may be assigned on more than one claim.

D          Subsequent encounter. This is an encounter after the active phase of treatment and when the patient is receiving routine care for the injury or poisoning during the period of healing or recovery.

S          Sequela. The 7th character extension ‘S’ is assigned for complications or conditions that arise as a direct result of an injury.

Combination Codes

One of the most significant changes in ICD-10-CM is the addition of combination codes in Chapter 19 Injury, Poisoning and Certain Other Consequences of External Causes for two code blocks. The code blocks are: T36-T50 Poisoning, adverse effects, and underdosing of drugs, medicaments and biological substances;  and T51-T65 Toxic effects of substances chiefly nonmedicinal as to source. These combination codes identify both the substance and the intent which includes accidental (unintentional), intentional self-harm, assault, undetermined, adverse effect, and underdosing. This means that there are no external cause codes for these conditions in the external cause chapter in ICD-10-CM.


This is just a short overview of some of the differences between ICD-9-CM and ICD-10-CM related to coding external causes of morbidity. For more information, see the 2012 ICD-10-CM Draft Code Set and the 2012 ICD-10-CM Official Guidelines and Reporting


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