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Comparison of the New Injury Severity Score and the Injury Severity Score

Tay, Seow-Yian MB, BS, FRCS(Ed)(A&E), FAMS; Sloan, Edward P. MD, MPH, FACEP; Zun, Leslie MD, FACEP; Zaret, Philip MD, FACS

Journal of Trauma-Injury Infection & Critical Care: January 2004 - Volume 56 - Issue 1 - pp 162-164
Original Articles

Background : The New Injury Severity Score (NISS) was proposed in 1997 to replace the Injury Severity Score (ISS) because it is more sensitive for mortality. We aim to test whether this is true in our patients.

Methods : This study was a retrospective review of data from 6,231 consecutive patients over 3 years in the trauma registry of a Level I trauma center studying outcome, ISS, and NISS.

Results : Misclassification rates were 3.97% for the NISS and 4.35% for the ISS. The receiver operating characteristic curve areas were 0.936 and 0.94, respectively. Neither the ISS nor the NISS were well calibrated (Hosmer-Lemeshow statistic, 36.11 and 49.28, respectively; p < 0.001).

Conclusion : The NISS should not replace the ISS, as they share similar accuracy and calibration.

Injury severity scoring is a cornerstone of trauma epidemiology. Since its introduction in 1974, 1 the Injury Severity Score (ISS), which is the sum of the squares of the single highest Abbreviated Injury Scale (AIS) score in each of the three most severely injured body regions, has become the standard summary measure of multiple injuries despite its limitation of one injury per body region.

In 1997, Osler et al., after tracing this restriction to a design limitation in the original study form used, introduced the New Injury Severity Score (NISS), defined as the sum of squares of the three highest AIS scores from each patient, regardless of body region. 2 This score was said to be associated with less misclassification and more favorable receiver operating characteristic (ROC) curves. The findings of Osler et al. were replicated in subsequent studies, 3,4 but not for pediatric trauma. 5 In this study, we aim to test whether these characteristics of the NISS (less misclassification and greater area under the ROC curve, compared with the ISS) apply to our patient population.

From the Department of Emergency Medicine, University of Illinois at Chicago (S.Y.-T., E.P.S.), and Departments of Emergency Medicine (L.Z.) and Trauma Surgery (P.Z.), Mount Sinai Hospital, Chicago, Illinois.

Submitted for publication July 15, 2002.

Accepted for publication January 13, 2003.

Address for reprints: Seow-Yian Tay, MB, BS, FRCS(Ed)(A&E), FAMS, Department of Emergency Medicine, Tan Tock Seng Hospital, Moulmein Road, 387980 Singapore; email:

© 2004 Lippincott Williams & Wilkins, Inc.