Measuring height for people with high body mass index at home: Standing up for inclusion

Introduction: Despite the population with body mass index (BMI) ≥40 kg/m2 increasing rapidly, current health survey data collection methods can exclude such people due to difficulties measuring height and weight. Accurate height measurement is vital in calculating BMI. If standard measures with a stadiometer are unsuitable due to physical disability, knee height or half-span can be used to infer height. Physical disability risk increases with obesity class. Method: For a broader study in a Scottish local authority area, people in receipt of health and social care services with likely BMI ≥40, were seen at home. Mobile participants were risk assessed for using a portable stadiometer and measured if able. Where unable or immobile, knee height and half-span were measured to infer height, using published calculations. Data collection was during the Covid pandemic, meaning measures had to be pragmatically achievable by one individual. Results: Measures were taken from 15 women and 10 men (n=25), aged 40-87 years, mean 62 (s=11.8), BMI range 40-77, mean 55 (s=10.4). The portable stadiometer was used for only one participant, due to its narrow base. Alternative measures gave diverse heights: 16 participants had ≥10cm discrepancy between knee height and half-span outcomes. 22 participants had gross lower leg oedema making knee height measures imprecise. Large body habitus impeded sternal notch location and arm straightening, making half-span measures inexact. Published equations were not representative of this population group. Taking participant's height either against a doorpost with a tape measure or recumbent height were pragmatic solutions for improved accuracy. Conclusions: For people with very high BMIs, their large body habitus, with related comorbidities means standard height measures can be invalid. Lack of measurement may obscure numbers affected. Improved portable stadiometer design should include a wider base, with a clear safe working load. Given the rise in this population, and their high health need, health survey methodology needs to ensure appropriate methods for their inclusion and accurate documentation, to enable appropriate future health service planning.