The American Association for the Surgery of Trauma Renal Grading System-Should Segmental Kidney Infarction be Classified as a Grade IV Injury?

In 2018 the American Association for the Surgery of Trauma revised renal injury grading. One change was inclusion of segmental kidney infarction under grade IV injuries. We aimed to assess how segmental kidney infarction will change the scope of grade IV injuries and compare bleeding control interventions in those with and without isolated segmental kidney infarction.We used high grade renal trauma data from 7 level 1 trauma centers from 2013 to 2018 as part of the Multi-institutional Genito-Urinary Trauma Study. Initial computerized tomography scans were reviewed to regrade the injuries. Injuries were categorized as isolated segmental kidney infarction if segmental parenchymal infarction was the only reason for inclusion under grade IV injury. All other grade IV injuries (including combined injury patterns) were categorized as without isolated segmental kidney infarction. Bleeding interventions were compared between those with and without isolated segmental kidney infarction.From 550 patients with high grade renal trauma and available computerized tomography, 250 (45%) were grade IV according to the 2018 American Association for the Surgery of Trauma grading system. Of these, 121 (48%) had isolated segmental kidney infarction. The majority of patients with isolated segmental kidney infarction (88%) would have been assigned a lower grade using the original 1989 grading system. Rate of bleeding control interventions was lower in isolated segmental kidney infarction compared to other grade IV injuries (7% vs 21%, p=0.002). Downgrading all patients with isolated segmental kidney infarction to grade III did not change the grading system's associations with bleeding interventions.Approximately half of the 2018 American Association for the Surgery of Trauma grade IV injuries have isolated segmental kidney infarction. Including isolated segmental kidney infarction in grade IV injuries increases the heterogeneity of these injuries without increasing the grading system's ability to predict bleeding interventions. In future iterations of the American Association for the Surgery of Trauma renal trauma grading isolated segmental kidney infarction could be reclassified as grade III injury.