Background: Nutrition screening and assessment tools often include body mass index (BMI) as a component in identifying malnutrition risk. However, rising obesity levels will impact on the relevancy and applicability of BMI cutoff points which may require re-evaluation. This study aimed to explore the relationship between commonly applied BMI cutoffs and diagnosed malnutrition. Methods: Data (age, gender, BMI and Subjective Global Assessment (SGA) ratings) were analysed for 1152 inpatients aged !65 years across annual malnutrition audits (2011e2015). The receiver operation characteristic (ROC) curve analysed the optimal BMI cutoff for malnutrition and concurrent validity of commonly applied BMI cutoffs in nutritional screening and assessment tools. Results: Malnutrition prevalence was 36.0% (n ¼ 372) using SGA criteria (not malnourished, moderate or severe malnutrition). Median age was 78.7 (IQR 72e85) years, median BMI 25.4 (IQR 21.8e29.7) kg/m 2 ; 52.1% male and 51.2% overweight/obese. ROC analysis identified an optimal BMI cutoff of <26 kg/m 2 , 80.8% sensitivity and 61.5% specificity (AUC 0.802, 95% CI 0.773, 0.830; p < 0.0001). Commonly applied BMI cutoffs (between 18.5 and 23 kg/m 2) failed to meet the alpha-priori requirement of 80% sensitivity and 60% specificity. However, BMI <23 kg/m 2 had the highest agreement (k ¼ 0.458) with malnutrition diagnosed using the SGA. Conclusions: Both malnutrition and overweight/obesity are common in older inpatients. Continuing increases in the prevalence of overweight and obesity will impact on the sensitivity of BMI as a screening component for malnutrition risk. The current study suggests tools developed over a decade ago may need to be revisited in future.

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