MRC135 - ICD10: Diagnostic Coding

Week 5: External Causes and Factors

ICD-10-CM has a code for "struck by sea lion."

Review Chapter 20 of your ICD-10-CM to review all the codes for external causes of morbidity.


The following readings will help you learn about the concepts covered this week.

Required Readings

  • Understanding Health Insurance, Chapter 6, “ ICD-10-CM Coding,” pp. 192-196
  • ICD-10-CM Index to External Causes
  • ICD-10-CM Tabular List of Diseases and Injuries:
    • Chapter 19, “Injury, Poisoning, and Certain other Consequences of External Causes”
    • Chapter 20, “External Causes of Morbidity”
    • Chapter 21, “Factors Influencing Health Status and Contact with Health Services”
  • ICD-10-CM Official Coding Guidelines for Coding and Reporting 2013, Sections I.C.19-I.C.21

Click the link below to access the required readings.

Chapter 6

Coding Injuries

Chapter 19 allows you to code the consequences of external causes acting on a patient’s body. These consequences include injury, poisoning, and complications of surgical and medical care. The S-section codes relate to single-body-site injuries; the T-section codes cover injuries to unspecified body regions, and are a “catchall” for all other circumstances of injury (such as poisoning). Therefore, if the injury was to one specific area of the body, you are likely to find the code in the S section, but if the injury affected more than one area of the body, you are likely to find the code in the T section.

For more information about assigning the proper injury or other circumstance code, click the link to access Click in the Search box and type “injury coding.”

Injury Coding

External Causes of Morbidity

Chapter 20 allows you to code the environmental factors that caused injury to the patient. These kinds of factors include accidents of many kinds (organized by the kind of vehicle involved), slipping/falling, exposure to mechanical forces, drowning, electrocutions, burns, self-harm, terrorism, assault, and abnormal reactions to surgical procedures—among others.

There are many terms in Chapter 20 used to describe specific players in accidents, answering questions such as: What is a driver, or a pedal cycle, or a public highway, or a three-wheeled motor vehicle?

After you have read over the introduction to Chapter 20, click the link to play a matching game and check your understanding of this terminology.

Drag-and-Drop Matching

Factors Influencing Health Status

Chapter 21, or Z codes, provide reasons for encounters; they require a procedure code if a procedure is performed. They are used when circumstances other than disease or injury are the reasons for the encounter. For example, when a patient is donating an organ or receiving some kind of limited care or service for a current condition, or when a patient has a problem that influences his health but is not a current illness. Z codes are assigned for patients seeking care for things such as:

  • Annual physical exams
  • Retained foreign body fragments
  • In vitro fertilization or other reproductive care
  • Screening for infectious and parasitic diseases, malignant neoplasms, or other reasons
  • Delivery of a baby
  • Fitting for artificial limbs
  • Cosmetic surgery

For a lighter look at ICD-10-CM coding, and to review what you’ve learned so far, check out the “ There’s a Code for That!” videos on YouTube, created by Click the link to access the YouTube website, search for "ICD-10 S Codes", and click on the link for the desired ICD-10 Code videos. (The codes relating to this unit are S, T, V, W, Y, and Z.) Which ones are your favorites? Post your thoughts in the Ask Your Instructor Forum.


Coding Practice

To summarize what you have learned, and to prepare for the graded coding assignment, complete the following coding practice activity. Click the link to download a document and practice assigning ICD-10-CM injury, external causes, and factors-related codes according to the guidelines.

Coding Practice

When you're ready, click the link to check your answers.

Coding Practice Answers