BMI upon discharge from hospital and its relationship with survival: an observational study utilising linked patient records.

Abstract

Current advice for patients being discharged from hospital suggests a body mass index of 18.5 to 24 kgm-2, although this aspirational target may often not be achieved. We examined the relationship between body mass index on discharge from hospital and subsequent mortality over a maximum follow-up of 3.8 years. We conducted a survival analysis using linked hospital records data with national hospital episode statistics and national death certification data. The analysis included adult patients who were admitted to University Hospitals Birmingham NHS Foundation Trust for a period of over 24 h during 2011, excluding day cases and regular day case attenders. The relationship between body mass index and mortality at medium term was estimated separately in both men and women, after accounting for case-mix. For both males and females, the relationship between body mass index at discharge and the loge hazard of death was strongly non-linear (p = 0.0002 for females and p < 0.0001 for males) and predictive (both p < 0.0001). In all models, the optimal body mass index range associated with best survival was 25 to 35 kgm-2, with a sharp increase in risk for lower body mass index. There was little evidence to support current aspirational body mass index targets in the discharge population. Hospitals should ensure adequate nutrition especially among those with a reduced body mass index.