Relationship of body mass index to subsequent mortality among seriously ill hospitalized patients

Objective: To determine if body mass Index (BMI = weight [kg]/height [m](2)), predictive of mortality in longitudinal epidemiologic studies, was also predictive of mortality in a sample of seriously ill hospitalized subjects. Design: Prospective, multicenter study. Setting: Five tertiary care medical centers in the United States. Patients: Patients greater than or equal to 18 yrs of age who had one of nine illnesses of sufficient severity to anticipate a B-month mortality rate of 50% were enrolled at five participating sites in the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT). Interventions: None. Measurements and Main Results: Patients were asked their current height and weight as part of the demographic data. Stratifying body mass index by percentile rank (less than or equal to 15, 15 to 85, and greater than or equal to 85th percentiles), risk ratios for mortality were calculated by Cox Proportional Hazards using the 15th to 85th percentile of body mass index as the reference group while controlling for multiple variables such as prior weight loss, albumin, and Acute Physiology Score. A body mass index in the less than or equal to 15th percentile was associated with an excess risk of mortality (risk ratio =1.23; p<.001)within 6 months. High body mass index (greater than or equal to 85th percentile) was not significantly related to risk of mortality. Conclusions: Body mass index, a simple anthropometric measure of nutrition employed in community epidemiologic studies, has now been demonstrated to be a predictor of mortality in an acutely ill population of adults at five different tertiary centers. Even when controlling for multiple disease states and physiologic variables and removing from the analysis all patients with significant prior weight loss, a body mass index below the 15th percentile remained a significant and independent predictor of mortality. Examination of patient vs. proxy data did not change the results. Future studies examining variables predictive of mortality should include body mass index, even in acutely ill populations with a poor probability of survival.