Patient risk factors for medical injury: A case-control study

Objective: To determine risk factors of medical injury, defined as untoward injury from diagnostic or therapeutic healthcare interventions. Identifying risk factors for medical injuries could inform the development of preventive interventions. Methods: A hospital-based case-control study. Cases and controls were selected among patients discharged from a large Midwestern teaching hospital between 1 January 2003 and 31 December 2004. Cases (n=268) were selected in a three-step process. First, medical injuries in the discharge database were identified using the Wisconsin Medical Injury Prevention Programme Surveillance Criteria. Second, provisional cases were randomly chosen from patients flagged with a medical injury. Provisional controls were randomly selected from patients not flagged with a medical injury, matching for Diagnosis Related Group of the provisional cases. Third, a chart review determined ultimate case-control status. Severity of illness and risk of mortality were calculated using the All Patients Refined-Diagnosis Related Groups system. Zahn's comorbidity score was calculated. Conditional logistic regressions were run with injury status as the dependent variable. Results: Among the 268 cases, 47.8% were procedure-related injuries and 44.8% were medication-related injuries. Conditional logistic regressions found higher severity of illness and higher risks of mortality were related to risk of medical injury (OR 3.29 (95% CI 1.05 to 10.31) and OR 5.16 (95% CI 1.42 to 18.79), respectively). Additional regressions showed the Zahn comorbidity score related to the risk of medical injury (OR 1.63, 95% CI 1.31 to 2.02). Conclusions: Patients with higher severity of illness, higher risk of inpatient mortality and multiple comorbidities are at increased risk for a medical injury.