ICD-coding of firearm injuries

James Harrison
NISU and Research Center for Injury Studies
Flinders University of South Australia
August 1997 (revised December 1997)

Summary

1. Current coding of deaths and admitted hospital cases due to firearm injury:

   • does not distinguish cases die to airguns, etc.;
   • includes some poorly defined categories and;
   • does not correspond to current Australian firearm license categories.

2. Forthcoming changes in coding (i.e., the introduction of ICD-10) will reduce the already limited information on the type of firearm involved in shooting injuries. Only handguns will be distinguished with any useful degree of specificity, and these account for a small proportion of cases in Australia.

3. Limited case information restricts the level of coding that is likely to be practicable without the introduction of special data collection systems. The extent of information available is being investigated.

4. Revised coding is proposed which:

   • Provides categories for airguns and related weapons.
   • Distinguishes the main types of firearms that produce injuries in Australia.
   • Retains compatibility with versions 9 and 10 of the ICD.
   • Is no more complex than the present system (i.e., ICD-9-CM).

Background

Shooting injuries account for about 500 deaths per year, and for a similar number of hospital admissions, in Australia.

Injuries resulting in death or in admission to a hospital are classified according to the International Classification of Diseases (ICD). The section of the classification used to code the firearm involved in producing an injury is the "External Cause" (E-code) chapter. At present (1997), deaths are coded by the ABS according to the basic WHO edition of the 9th revision of the ICD (ICD-9), and hospital separations are coded according to the second Australian edition of the Clinical Modification of the ICD (Australian ICD-9-CM).

The level of detail provided by ICD-9 on the type of firearm involved is similar for each of the main "human intent" categories distinguished in ICD-9: accident, self-inflicted injury, assault, and undetermined intent (Table 1). ICD-9 and Australian ICD-9-CM codes for shooting cases are, at present, identical. The next edition of the classification, ICD-10, provides less information on the type of firearm than ICD-9, handguns being the only type given a relatively specific category (Table 2).

Plans are in place to introduce ICD-10 in Australia in the near future. The date of introduction for coding hospital separations is 1 July 1998. Hospital separations coding will initially use the first Australian Modification of ICD-10, to be published soon by the National Center for Classification in Health. (The sections of interest here are the same as in the standard edition of ICD-10.)

Table 1: Coding of firearms in ICD-9 and Australian ICD-9-CM

* "shotgun (automatic)" for E922.1 (There is no obvious reason for the difference in wording)

"part" means that other types of case are also coded to the category.

"Accidental" injury due to an air rifle or BB gun is coded to E917.9 (Striking against or struck accidentally by object or person-other)

"Military firearm" and "hunting rifle" are not further defined.

Table 2: Coding of firearms in ICD-10

Firearm coding categories chosen for use should be useable in hospital settings. Clinical information is of two main types

• History: a description provided by the patient, or other witness.
• Examination: the observed nature of the injury (and sometimes the projectile that produced it).

The appearance of firearm wounds usually provides some information about the nature of the weapon that produced it (e.g., rifle vs. shotgun). However, some distinctions that might be of interest for purposes of monitoring and research cannot be made reliably on the basis of the wound, or examination of the bullet that produced it (if available). For example, Category C and Category D of the Australian firearm license categories are distinguished only by the magazine capacity of weapons. Furthermore, weapons in these two categories are distinguished from weapons in categories A and B by whether or not they are self-loading (or pump action). Neither of these characteristics of weapons can be deduced reliably from the clinical features of a wound.

If such information is to be recorded, it must be based, solely or in part, on information provided by a witness (including the injured person, if surviving), or an investigator. Clinical history may or may not provide information about the nature of the firearm, depending on the condition and knowledge of the patient and the circumstances of the shooting.

Shooting deaths are generally investigated by police and assessed and certified by a coroner. About four-fifths are recorded as suicides and another 5 percent are found to be accidental. One might expect that the firearm would be readily available for assessment in these cases. Surprisingly, about 30 percent of firearm suicides and about 40 percent of accidental firearm deaths between 1979 and 1995 were given the E-code meaning "Firearm – other or unspecified."

Implications

The introduction of ICD-10 will reduce the already limited information on the type of firearm involved in shooting injuries. Only handguns will be distinguished with any useful degree of specificity. Handguns account for a small minority of shooting cases in Australia (about 5 percent or less of shooting deaths and less than 20 percent of cases admitted to a hospital.)

Airgun shootings are not distinguished under either ICD-9 or ICD-10. "Accidental" airgun shooting moves from the residual category of "Striking against or struck accidentally by object or person - other" under ICD-9 to the residual categories for "Discharge from other and unspecified firearms" under ICD-10. There is no defined place for coding injury due to gas (not air) or spring powered guns in either edition of ICD.

Two of the categories provided under ICD-9-CM are poorly defined and pose difficulties for coding and for interpretation.

The ICD categories do not take account of the current Australian firearm license categories (See Attachment 1).

The extent, specificity and reliability of source information is uncertain, and is likely to differ substantially between sites (e.g., coroner systems vs. hospitals) and cases (e.g., a firearm homicide or wounding in which the firearm has not been recovered vs. a suicide in which the firearm is available for inspection.).

Aim

Propose changes to the coding of firearm injuries which will:

• Provide categories for airguns and related weapons.
• Retain compatibility with versions 9 and 10 of the ICD.
• Are practicable for use by hospital coders.
• Distinguish the main types of firearms that produce injuries in Australia.
• Take account of the Australian firearm license categories.

Proposal

Code firearm injury cases in Australian hospital separations (preferably also deaths data) according to the approach shown in Attachment 2. This approach:

• Provides categories for airguns and related weapons.
• Distinguishes the main types of firearms that produce injuries in Australia.
• Is no more complex than the present system (ie ICD-9-CM).
• Defines the designated types of weapon in simple and specific terms. (See Attachment 3)
• Is compatible with versions 9 and 10 of the ICD. (See Attachments 4 and 5)
• Provides codes to enable the same types of firearms to be distinguished in each of the "intent" sections of the classification.

This approach provides only limited compatibility with the Australian firearm license categories. In particular, it does not draw distinctions based on whether a weapon is self-loading (required to separate Category C and D weapons from others), nor on magazine capacity (required to distinguish between Category C and Category D).

Implementation of the approach under ICD-9-CM would require redefinition of the (currently poorly defined) categories "hunting rifle" and "military firearm."

Implementation of this model as part of ICD-10-AM will require a supplementary coding field (i.e., a fourth character). This is because the ICD-10 Chapter XX classification (the section that covers external causes) has been structured in a way that provides fewer code categories than the equivalent part of ICD-9 and leaves little room for expansion within the basic structure.

Further information will be sought on the extent of information on firearm type that is recorded in medical records. The findings will guide further steps. These may include efforts to improve the information about firearms that is recorded, revision of the classification to accommodate practicalities of clinical practice, and further development of the classification to specify firearms in terms of the Australian firearm license categories (for example, to distinguish self-loading and pump-action long-guns from other types)

Attachment 1: Australian Firearm License Categories in relation to suggested firearm injury coding categories

Attachment 2: Proposed revised coding of firearms

Revised coding of firearms – ICD-9

Revised coding of firearms – ICD-10

NOTES:

Both tables

• "Handgun": includes air pistol and shortened ("sawn-off") long guns.
• "Nonpowder" actuated long guns: includes air rifles and other gas or spring operated long guns.
• "Shotgun" and "rifle" include pump-action and self-loading types.

Table 3

• Use the values in the body of the table as 4th digits for the E-codes shown in the second column.
• Alter the coding rule for accidental injury due to an air rifle: use E922.7, not E917.9 (part).
• Injury due to war operations by bullets and fragments (E991): alter use of E991.0, E991.1 and E991.2 as shown in Table 3. Retain standard use of E991.3 and E991.9.

Table 4

• Use the values in the body of the table as an additional digit for the codes shown in the second column. This could be an additional character or a separate field.
• Standard ICD-10 codes W32, X72, X93 and Y22 could be used in place of W34/1, X74/1, X95/1 and Y24/1. ICD-10 codes W33, X73, X94, and Y23 are not required.

Attachment 3: Suggested wording of category descriptions

Attachment 4: Mapping revised firearm category codes to standard ICD-9-CM

* Airgun cases

** Redefined. Model A: "Rifle, .22 or smaller"; Model B: "Rifle, not self-loading"

*** Redefined. Model A: "Rifle, larger than .22"; Model B: "Rifle, self-loading"

Attachment 5: Mapping proposed revised firearm codes to standard ICD-10