Revision of the International Classification of Diseases to include standardized descriptions of multiple injuries and injury severity.

Introduction The International Classification of Diseases (ICD) is widely used as a source of mortality statistics. However, two major difficulties arise when recording, presenting and analysing injury data using this diagnosis classification. First, due to the absence of standardized methods for describing multiple injuries, they are described in various ways in mortality and morbidity statistics. For example, designating the most severe injuries as the primary injuries or categorizing multiple injuries as such without further details. (1) Second, an increasing need to describe injury severity for case-mix groups has led to the introduction of various additional severity-scoring methods, as the ICD itself, as a diagnosis classification for mortality, does not consider severity. To avoid the costs of additional severity scoring, methods have been developed to convert administrative ICD-based diagnosis codes into severity scores using computer software of to calculate survival probability for each diagnosis code from patient data. However, these approaches have respective disadvantages due to the need to track software updates or the need for large data sets to calculate the probabilities. (2) The World Health Organization (3) is currently advocating revision of the ICD to expand upon its largely administrative applications and allow more clinical uses. This provides an opportunity to address the issues associated with describing multiple pathologies and scoring the severity of injury data, which are also relevant to other non-injury diseases. In addition, a few low-income countries do not use the ICD of severity scores, even in the absence of vital registrations depending on periodical surveys; (3) thus the revision process should facilitate their adoption of standardized methods. Here we discuss how the revised ICD system could standardize the description of multiple injuries to provide accurate statistics, incorporate severity scores to avoid additional resource input, and facilitate utilization in countries where it is not currently in use. Describing multiple injuries For mortality statistics, the one-dimensional principle of the ICD allows only one underlying cause of death to be selected and coded. The multi-dimensional phenomenon of multiple injury is thus usually reduced either to a single code reflecting the primary (most severe) injury or to one of a few multiple-injury codes, based upon an arbitrary decision. (1,4) Selecting the primary injury when filling in death certificates, or the underlying cause from among several injuries reported in death certificates, is also an arbitrary practice that reflects the certifier's of coder's perception of which pathology is the most important. Choosing just one code results in a loss of information on the other, unselected, pathologies, so the resultant statistics underestimate the significance of each injury and inadequately depict the interactions between them. (1) The limited number of multiple-injury codes included in the ICD cannot cover all possible patterns. For example, codes T00-T07 indicate injuries involving multiple body regions while S codes also include multiple injuries in the same body regions, (e.g. S52.7 indicates "multiple fractures of the forearm"). This arbitrariness, due to a lack of standardization, also applies to the presentation and analysis of morbidity statistics, (1) although not to the way that they are recorded because clinical modifications of the ICD require the coding of each injury, thereby superseding the multiple-injury codes. The shortcomings of one-dimensional coding have led some countries to introduce multiple coding systems for mortality statistics, in which all causes mentioned on a death certificate are coded and reported. (4) It would be preferable to omit the multiple-injury codes from the revised ICD, and to code and record all injuries separately. This would allow all patients with a certain injury to be counted, even when it is not the primary injury, which is not the case with one-dimensional underlying-cause (of primary-injury) coding. …