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Pre‐procedural considerations

Check that the patient is able to stand or sit on the appropriate scales. The patient should remove outdoor clothing and shoes before being weighed and having their height measured.

When obtaining a height measurement, check that the patient is able to stand upright while the measurement is taken. For patients who are unable to stand, height may be determined by measuring ulna length and using conversion tables (see Figure 8.12). If neither height nor weight can be measured or obtained, BMI can be estimated using the mid‐upper arm circumference (MUAC) (BAPEN [14], Benítez Brito et al. [22]). It may not be possible to weigh patients who cannot be moved or are unable to sit or stand. Alternative methods to obtain weight should be explored, for example bed scales (which can be placed under the wheels of the bed), scales as an integral part of a bed or a patient hoist with a weighing facility.

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Figure 8.12 Conversion chart for estimating height from ulna length. Source: Reproduced from BAPEN ([15]) with permission.

Equipment

Scales

Scales (either sitting or standing) must be calibrated and positioned on a level surface. If electronic or battery scales are used then they must be connected to the mains or have appropriate working batteries prior to the patient getting on the scales.

Stadiometer

These are devices for measuring height and may be mounted on weighing scales or wall mounted.

Tape measure

This is required if estimating height from ulna length or MUAC or for measurement of waist circumference. The tape measure should use centimetres, and it must be disposable or made of plastic that can be cleaned with a detergent wipe between patient uses.

Assessment tools

Identification of patients who are malnourished or at risk of malnutrition is an important first step in nutritional care. There are a number of screening tools available that consider different aspects of nutritional status. National screening initiatives have demonstrated that 25% of patients admitted to hospital were found to be at risk of malnutrition – 18% high risk and 7% medium risk (BAPEN [9]). Particular diagnoses, such as cancer, increase the risk of malnutrition.

All patients who are identified as at risk of malnutrition should undergo a nutritional assessment. Subjective Global Assessment (SGA) and patient‐generated SGA (PG‐SGA) are comprehensive assessment tools that necessitate more time and expertise to carry out than most screening tests and therefore are more likely to be used by those with specialist skills, for example dietitians. The Malnutrition Universal Screening Tool (MUST) (BAPEN [14]) is an example of a screening tool that is based on the patient's BMI, weight loss and illness score; it is less time consuming and easier to use. Other tools may be specific to the patient's age or diagnosis; for example, the Mini Nutrition Assessment (MNA) is used in the elderly and the Royal Marsden Nutrition Screening Tool is used for patients with cancer (Kondrup et al. [77], Shaw et al. [166]). The most important feature of using any screening tool is that patients identified as having a nutritional deficit or concern, or as requiring intervention have a nutritional care plan initiated and are referred to a dietitian for further advice if appropriate.

Measurement of waist circumference

Table 8.8 shows the waist circumference measurements for men and women at which there is an increased relative risk of heart disease, type 2 diabetes and cancer. In some populations, waist circumference may be a better indicator of risk than BMI, e.g. in persons of Asian descent. In very obese patients (those with a BMI above 35 kg/m²), waist circumference adds little to the predictive power of disease risk (National Obesity Forum [106]).

Table 8.8 Waist circumference measurements

	Increased risk	Substantially increased risk
Men	≥94 cm	≥102 cm
Women	≥80 cm	≥88 cm

Procedure guideline 8.8

Measuring the weight and height of a patient

Table 8.9 Prevention and resolution (Procedure guideline 8.8)

Problem	Cause	Prevention	Action
Patient unable to stand on scale	Poorly positioned scales. Patient balance not sufficient.	Prior to asking the patient to stand on the scales, check with them whether they are able to do so. Offer sitting scales if necessary.	Ensure both sitting and standing scales are available in the hospital.
Weight obtained appears too low	Patient may have put pressure on the scales prior to them reaching zero.	Ensure zero is visible before patient touches scales.	Check weight with patient once obtained. Reweigh patient to check correct weight.
Weight obtained appears too high	Patient may be wearing outdoor clothes or shoes or be carrying a bag, drainage bag and so on. Patient may have fluid retention, for example oedema or ascites.	Ensure that the patient is wearing only light indoor clothes before standing on the scales. Check whether patient has fluid retention. Ask patient to empty any drainage bags.	Check weight with patient once obtained. Reweigh patient to check correct weight.
Patient is unable to stand for height measurement	Patient is unwell or has a physical disability.	Discuss the procedure with patient before undertaking height measurement.	Consider estimating height from ulna measurement.
Difficulty obtaining waist circumference in obese patients	Tape measure may not be long enough. Difficulty identifying the correct position to measure waist circumference.	Calculate BMI and if it exceeds 35 kg/m² then do not measure waist circumference.	Use BMI alone.

BMI, body mass index.