Research Article: Comparison of injury severity scores (ISS) obtained by manual coding versus “Two-step conversion” from ICD-9-CM

Date Published: May 1, 2019

Publisher: Public Library of Science

Author(s): Rebeca Abajas-Bustillo, Francisco José Amo-Setién, César Leal-Costa, María del Carmen Ortego-Mate, María Seguí-Gómez, María Jesús Durá-Ros, Mark R. Zonfrillo, Belinda J. Gabbe.


The International Classification of Diseases (ICD) is the standard diagnostic tool for classifying and coding diseases and injuries. The Abbreviated Injury Scale (AIS) is the most widely used injury severity scoring system. Although manual coding is considered the gold standard, it is sometimes unavailable or impractical. There have been many prior attempts to develop programs for the automated conversion of ICD rubrics into AIS codes.

To convert ICD, Ninth Revision, Clinical Modification (ICD-9-CM) codes into AIS 2005 (update 2008) codes via a derived map using a two-step process and, subsequently, to compare Injury Severity Score (ISS) resulting from said conversion with manually coded ISS values.

A cross-sectional retrospective study was designed in which medical records at the Hospital Universitario Marqués de Valdecilla of Cantabria (HUMV) and the Complejo Hospitalario of Navarra (CHN), both in Spain, were reviewed. Coding of injuries using AIS 2005 (update 2008) version was done manually by a certified AIS specialist and ISS values were calculated. ICD-9-CM codes were automatically converted into ISS values by another certified AIS specialist in a two-step process. ISS scores obtained from manual coding were compared to those obtained through this conversion process.

The comparison of obtained through conversion versus manual ISS resulted in 396 concordant pairs (70.2%); the analysis of values according to ISS categories (ISS<9, ISS 9–15, ISS 16–24, ISS>24) showed 493 concordant pairs (87.4%). Regarding the criterion of “major trauma” patient (i.e., ISS> 15), 538 matching pairs (95.2%) were obtained. The conversion process resulted in underestimation of ISS in 112 cases (19.9%) and conversion was not possible in 136 cases (19%) for different reasons.

The process used in this study has proven to be a useful tool for selecting patients who meet the ISS>15 criterion for “major trauma”. Further research is needed to improve the conversion process.

Partial Text

The Abbreviated Injury Scale (AIS), developed by the Association for the Advancement of Automotive Medicine (AAAM), is the most widely used injury severity scale in the world. It is defined as “an anatomically-based, consensus-derived, global severity scoring system that classifies each injury by body region according to its relative importance on a 6-point ordinal scale”[1]. This scale measures severity of single injuries. In order to assess the overall severity of patients with multiple injuries, the Injury Severity Score (ISS) [2] and the New Injury Severity Score (NISS) [3] were developed, based on the AIS.

A cross-sectional retrospective observational study was designed, in which medical records at the Hospital Universitario Marqués de Valdecilla of Cantabria (HUMV) and the Complejo Hospitalario of Navarra (CHN) were reviewed from February 2012 to February 2013. These are third level hospitals (equivalent to trauma centre hospitals) in two autonomous communities in the north of Spain, with similar population characteristics. The study was approved by the Clinical Research Ethics Committee of Cantabria (reference number 2015.246) All data were fully anonymized and informed consent was no required.

Out of the 750 patients initially reviewed, 51 were excluded: two of them because their medical records could not be accessed and the remaining 49 because they did not meet the inclusion criteria. Therefore, the final sample consisted of 699 subjects, 49.30% (n = 344) from HUMV and 50.70% (n = 355) from CHN. In the final sample, 388 were male (55.50%) and 311 female (44.40%). The mean age was 52.70 years (SD = 29.20), ranging from 0–98 years. Table 1 includes the descriptive statistics of the sample population.

As said before, AIS and ICD are two classification systems with different lexicon and purposes. Both are relevant for injury research in order to identify the frequency and severity of injuries, monitor trends and develop prevention strategies. For these reasons, several attempts have been made to create conversion programs; the current study is one of such investigations.

The results show that the conversion program that converts ICD codes into AIS codes performs similarly to manual coding. The observed agreement between manual and converted ISS was “good” with the chosen classification system. The kind of injured patients could facilitate those results. We have developed a method that enables the selection of “major trauma” patients, defined as those with ISS>15, in 95.2% of cases where conversion was possible. This conversion process could be useful for the identification of major trauma patients (understood as those with an ISS>15) within a certain sample or database, for research or reimbursement purposes. The authors recommend its use just when manual coding is impractical or is not available and being conscious of the information lost in the process.




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