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Not adjusting for pre-existing health problems may have exaggerated the number of deaths due to medical injury

In 2002, nearly 14 percent of adults hospitalized in Wisconsin suffered a care-associated medical injury which was believed to have increased their risk of dying by 48 percent compared with other patients. Researchers used the Wisconsin Medical Injuries Prevention Program (WMIPP) screening criteria to identify medical injuries (harm associated with a therapeutic or diagnostic healthcare intervention) among all 562,317 patients discharged from 134 acute care hospitals in Wisconsin in 2002. A total of 77,666 (14 percent) of discharges met WMIPP criteria for at least one medical injury. Overall, deaths occurred among 3.14 percent of those who suffered a medical injury and 2.13 percent of those who had no medical injury diagnosis upon discharge (a 48 percent difference).

However, after adjustment for patients' coexisting illnesses, severity of illness, and other factors (baseline mortality risk), the excess risk of dying associated with medical injury disappeared. The only types of medical injuries that were still associated with increased odds of dying were related to procedure-related complications or to a device, implant, or graft. Both medical injury and in-hospital mortality risks were higher among older patients who had multiple coexisting medical problems at admission.

These findings suggest that previous unadjusted risks of dying attributable to medical injury, which did not account for patients' baseline mortality risk, may have exaggerated the number of deaths due to medical injury. In this study, researchers adjusted for baseline risk of death using an index of coexisting disease, age, sex, diagnosis, hospital characteristics, and clustering within hospital. Injuries related to procedures or to a device, implant, or graft were still associated with increased adjusted odds mortality of 39 percent and 16 percent, respectively. The study was supported in part by the Agency for Healthcare Research and Quality (HS11893).

See "Excess mortality caused by medical injury," by Linda N. Meurer, M.D., M.P.H., Hongyan Yang, M.S. Clare E. Guse, M.S., and others, in the September 2006 Annals of Family Medicine 4(5), pp. 410-416.

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