Agreement Between Standard and ICD-10-Based Injury Severity Scores

Injury Severity Score (ISS) is used to describe anatomical lesions. ISS is traditionally determined through medical record review (standard ISS), which requires specific training and may be time-consuming. An alternative way to obtain ISS is by use of ICD-9/10 injury diagnoses, and several conversion tools exist. We sought to evaluate the agreement between standard ISS and ISS obtained with two tools converting ICD-10 diagnoses.

Our cohort consisted of trauma patients ≥18 years admitted to Rigshospitalet between 1999 and 2016. The included patients had standard ISS recorded in the Trauma Audit and Research Network (TARN) database (ISS-TARN), and ICD-10 injury diagnoses for the trauma contact were recorded in the Danish National Patient Registry. We used the tools ICDPIC-R and ICD-AIS map to calculate ISS based on ICD-10 diagnoses. ICDPIC-R provided two ISSs: ISS-TQIP and ISS-NIS. The ICD-AIS map resulted in one ISS: ISS-map. The ISS-TARN was compared to the conversion tool ISSs using Bland-Altman plots. The agreement between ISS-TARN and the conversion tool ISSs for ISS above 15 was assessed using kappa statistics (κ).

We included 4308 trauma patients. The median age was 44 years, 70% were male, and 92% had a blunt injury mechanism. The median ISS-TARN was 16 [IQR: 9-25], and the median conversion tool ISSs were 10 [2-25] (ISS-TQIP), 17 [5-26] (ISS-NIS), and 9 [4-16] (ISS-map). The Bland-Altman plots all showed increasing difference in ISS with increasing mean ISS. Bias ranged from -7.3 to 1.1 and limits of agreement ranged between -28.0 and 25.7. The agreement for ISS above 15 was fair to moderate (κ = 0.43 (ISS-TQIP), 0.44 (ISS-NIS), and 0.29 (ISS-map)).

Using ICDPIC-R or ICD-AIS map to determine ISS is feasible, but limits of agreement were unacceptably wide. The agreement between ISS-TARN and ICDPIC-R was moderate for ISS above 15.