Date Published: May 16, 2019
Publisher: Public Library of Science
Author(s): Laura V. White, Nathaniel Lee, Flora P. Marin, Naomi R. Saludar, Tansy Edwards, Sharon E. Cox, Wisit Cheungpasitporn.
Body mass index (BMI) kg/m2 is a key screening tool for under-nutrition in adults, but difficult to obtain in immobile or unwell patients, particuarly in low resource settings, due to inability to accurately measure both weight and height. Mid-upper arm circumference (MUAC) is used to assess under-nutrition in children under 5 years but no standardised cut-off values exist for adults. In a cohort of adult Filipino patients admitted to a tuberculosis ward we assessed (i) cut-offs for MUAC to predict moderate under-nutrition (BMI <17kg/m2), (ii) the performance of limb lengths to predict height and; (iii) associations of body fat percentage from skinfolds and hand grip-strength with BMI. In 303 patients with MUAC and BMI at admission, aged 18–80 years (mean = 45.5, SD:14.8), BMI ranged from 11.2–30.6 kg/m2 and 141 (46.5%) had BMI <17.0 kg/m2. Using receiver operator curves, MUAC cut-offs were identified as <20.5cm for males (sensitivity: 89%, specificity: 84%) and <18.5cm for females (sensitivity: 91%, specificity: 89%), for BMI<17.0 kg/m2. Using published equations, knee height had the lowest mean difference between predicted and measured heights compared to ulnar or demi-span: (-0.98 cm, 95% CI: -1.51/-0.44). Both grip-strength and body fat percentage were positively associated with BMI, in separate linear regression models with exposure-age-sex interactions (adjusted-R-squared values: 0.15, 0.66, respectively). MUAC can predict moderate acute under-nutrition with high positive predictive value. Further research is required to determine the performance of alternative measures to BMI to predict mortality or adverse outcomes in acutely unwell patients.
Under-nutrition is a common risk factor for mortality among hospitalized patients  in both low and high resource settings. Under-nutrition is also associated with prolonged length of stay, increased likelihood of re-admission  and higher risk of infections . Early diagnosis and intervention for under-nutrition can result in reduced costs, morbidity and mortality [4, 5]. Therefore, screening for under-nutrition on admission, to identify patients at risk and those who require nutrition interventions should occur for all patients. Several ‘nutrition scores’ such as the subjective global assessment (SGA) and the malnutrition universal screening tool ‘MUST’ exist but rely on body mass index (BMI) to determine accurate risk classification . Although BMI is widely used in nutrition screening, obtaining accurate weight or height measurements among severely unwell or immobile inpatients is often not feasible. Therefore, the use of BMI as an indicator is a barrier to identification of under-nutrition in acutely unwell or immobile patients. Some tools like the MUST provide alternative measures for patients where height, or height and weight cannot be obtained, such as the use of limb length and predictive equations to determine height and the use of mid-upper arm circumference (MUAC) in the absence of weight . However, the majority of these predictive equations have been generated using Caucasian participants and studies have demonstrated these equations may not predict height as accurately in other ethnicities [8, 9]. For immobile patients, limb length predictive equations still require the estimation or self-reporting of an accurate weight to determine BMI and in many hospitalized patients recent weight loss renders their ‘usual weight’ inaccurate. When both weight and height are unavailable, alternative measures such as MUAC have been investigated in place of BMI . However, despite a systematic review and individual participant data meta-analysis on the possible MUAC cut-off to identify under-nutrition, as defined by the WHO cut off of <18.5 kg/m2,  there are still no internationally recognized cut-off values for MUAC to define under-nutrition in adults. This study evaluated alternative methods to reliably diagnose moderate and severe under-nutrition in an acutely unwell Filipino in-patient population. Among the study population typical diagnosis based on BMI were not possible for a substantial proportion of patients. Patients who could not be diagnosed using BMI likely represent those with advanced clinical disease and were therefore at a greater risk of malnutrition and poor clinical outcome. Source: http://doi.org/10.1371/journal.pone.0215968