Association between underweight and hospitalization, emergency room visits, and mortality among patients in community medical homes

BACKGROUND In older adults, underweight (body mass index [BMI] <18.5) has been associated with increased mortality. This increased mortality risk may be associated with increased health care utilization. We evaluated the relationship between underweight and hospitalization, emergency room visits, and mortality. METHODS An analysis of a retrospective cohort study was conducted at a multisite academic primary care medical practice in Minnesota. The patients were ≥60 years of age, impaneled within primary care on January 1, 2011, and had a BMI measurement recorded between January 1, 2011, and December 31, 2011. Individuals were excluded if they refused review of their medical record. The primary measurement was BMI, which was categorized as underweight (BMI < 18.5) or normal and obese (BMI ≥ 18.5). The outcomes were hospitalization, emergency room visits, and mortality in the 2011 calendar year. Associations between underweight and each outcome were calculated using logistic regression. Interactions between underweight and gender were assessed in the logistic regression models. The final results were adjusted for age, gender, comorbid health conditions, and single living status. RESULTS The final cohort included 21,019 patients, of whom 220 (1%) were underweight. Underweight patients had a higher likelihood of hospitalization compared with patients with higher BMI (adjusted odds ratio [OR] 1.64; 95% confidence interval [CI] 1.21-2.22). Underweight patients were also more likely to visit the emergency room (adjusted OR 1.70; 95% CI 1.28-2.25) or to die (adjusted OR 3.64; 95% CI 2.33-5.69). Men with a BMI < 18.5 compared with those having a BMI ≥ 18.5 had the highest odds of hospitalization (OR 3.45; 95% CI 1.59-7.48). CONCLUSION Underweight older adults, especially men, have higher odds of hospitalization, emergency room visits, and mortality. Future work on underweight might involve improving weight status, which may reduce the risk of hospitalization, emergency room visits, and mortality.