There are standard procedures for skinfold thickness measurements (Lee and Nieman, 1996), which can be taken at a number of sites including the abdomen, thigh, chest and below the scapula, although the triceps is the most accessible. BMI does not distinguish fat from muscle protein. Obesity is defined as values above 30kg/m 2.
Based on mortality and morbidity tables, adults are often considered underweight and/or malnourished at less than 18.5kg/m 2 although in older people a higher cut-off (possibly 23kg/m 2) may be indicated, due to relative changes in body composition with ageing (Beck et al, 1998). At least four versions of BMI are available but Quetelet’s Index, weight (kg) / height (m 2), is most often used for adults and Ponderal’s Index, height (m)/ weight (kg ^-3) for children (Lees et al, 1995). Weight alone takes no account of frame size this is achieved in combination with height as the body mass index (BMI). Calculation of percentage of usual body weight Body mass index However, while commonly used, many of these are dated and American in origin, and it is not clear how applicable they are for individual people in the UK.īox 4. Calculation of percentage weight changeĬurrent weight can also be compared to usual weight, if this is known (Box 4), and tables of ideal or reference weights. (NB all measurements must be in the same scale, e.g. Previous/ usual body weight – current weight x 100 Loss of >5% over one year has been linked with increased mortality (Wallace et al, 1995). Significant weight loss has been suggested as >5% loss in one month or >10% in six months, although 5–10% loss may indicate nutritional ‘risk’. Percentage weight change can be calculated (Box 3). Weight by itself is difficult to interpret, although change over time may be more informative. Clothing, fluid balance including diurnal or monthly cycles, oedema and dehydration, tumor-load and alterations of drug prescriptions are all influential. Accurate measurement requires regularly calibrated and maintained scales capable of accommodating bed-bound people. Calculating height from knee-height WeightĪlthough weight is extensively used as a nutritional measurement both for assessment and monitoring, its limitations are well-recognised. Height in cm = (1.83 x knee-height cm) – (0.24 x age years) + 84.88 Illustrations of these measurement approaches are available in the explanatory guide to the Malnutrition Universal Screening Tool (Elia et al, 2003). Calculations for height approximations (Box 2) and nomograms are available(Chumlea et al, 1985 Haboubi et al, 1990). This may be measured either lying supine with the knee flexed at 90 o using knee-height calipers (Chumlea et al, 1985) or in the seated position using a stadiometer (Haboubi et al, 1990). The length from the point of the elbow (the olecranon) to the mid-point of the prominent bone of the wrist (the styloid process) is then measured using a tape measure. This is measured with the arm bent up across the chest (preferably the left side), with the palm flat across the chest and fingers pointing to the opposite shoulder. Height in cm = (1.4 x demi-span cm) + 57.8 Height in cm = (1.35 x demi-span cm) + 60.1 A calculation (Box 1) provides a ‘height’ value (Bassey, 1986). This is measured with the arm outstretched straight, palm forwards, from the base of the middle/ ring fingers to the sternal notch using a non-stretch tape measure. Both have error margins of around 4cm but may be useful and acceptable with frail people.
Recalled or reported height may also be used but these risk incurring wide margins of error.Īlternative methods provide ‘height’ measurements for BMI calculation. Equipment may not be available, many hospital patients cannot stand and it is not clear how measurements should be interpreted in people who have experienced height loss, kyphosis or scoliosis. However, accurate measurement requires the subject to stand erect under a stadiometer, which can be problematic. It is also required to calculate body mass index (BMI). This is most commonly used as a nutritional index with children, with height measurement two standard deviations below median height for age-defining stunted growth.