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Nutritional screening and assessment

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Lin Perry, PhD, MSc, RGN, RNT, is senior research fellow, St Bartholomew School of Nursing and Midwifery, City University.

Nutritional screening is a first-line process of identifying patients who are already malnourished or at risk of becoming so; nutritional assessment is a detailed investigation to identify and quantify specific nutritional problems (Bond, 1997). 

Nutritional screening is usually undertaken by nurses and doctors; assessment by dietitians.

Why is it done?

Good nutrition is fundamental for health, healing and recovery from illness and injury. Malnutrition is associated with muscle wasting, impaired respiratory and cardiac function, decreased mobility (Lennard-Jones, 1992); susceptibility to infection and delayed wound healing(Chandra, 1990; Windsor et al, 1988); depression and lethargy (Brozek, (1990). Hospital complications, mortality and unplanned readmission rates rise, inpatient treatment is prolonged (Robinson et al, 1987; Sullivan, 1992). Many factors including disease predispose to malnourishment and indicators of malnutrition are found in up to 40% of patients admitted to hospital and a significant proportion of community patients (McWhirter and Pennington, 1994; Edington et al 1996). Screening, by identifying patients and clients with problems or at risk of developing them, is the essential first step of management.

How is it done? 

There are many screening methods but all have limitations, especially when used with acutely ill patients. No single measurement is adequate.

Clinical examination

This is an important component but while malnutrition produces a range of clinical signs (Bond, 1997) these tend to be subtle and non-specific until malnutrition is advanced. Reliance upon clinical signs for nutritional screening may not be effective.

Weight

This is commonly used, in a variety of ways:

Compared with percentile weight tables;

Compared with ideal weight tables;

Compared with previous/ usual weight.

Sequential weights can be recorded to track progress/ response to nutrition support.

Comparing current weight with tables of percentiles of weight by age and sex (Frisanco, 1990) (Box 1) indicates, for example, that a 70-year-old woman weighing 45kg is among the lightest 5% of women her age. However, these measurements come from US studies in the 1970s and it is not clear how applicable they are for British people today. 

Percentiles of weight (kg)

5 10 25 50 75 90 95

Males

4044.9 years 60.7 64.3 71.9 79.6 89.4 98.8 104.8

7074.9 years 53.9 57.5 65.2 73 81.3 90.4 95.9

Females

4044.9 years 49.2 51.8 57 64 75.1 89.8 99.1

7074.9 years 46.5 50.1 57 64.5 74.4 83.3 88.8

 

Box1. Examples of percentile values for weight according to age and sex

Tables of ideal weights, associated with longevity, can be similarly used but are also American in origin (Metropolitan Life Foundation, 1983). Current weight can be compared to previous records, known or usual weight and percentage weight change over a time period calculated (Box 2). Weight loss of 5% or more over one month is significant but rate of loss is also important with faster rate indicating more acute problems (Blackburn et al, 1977) (Box 3).

Weight today = 55kg; weight 1 month ago = 60kg.

% weight change:

usual or previous weight minus current weight x 100

usual or previous weight

So % weight change = 60 - 55 x 100 = 8.3% weight loss in 1 month

60

Box2. Example of calculating weight change 

Significant Severe 

weight loss weight loss

Time (%) (%)

1 week 1-2 >2 

1 month 5 >5

3 months 7.5 >7.5

6 months 10 >10

Box3. Evaluating percentage weight change

Weight has limitations as a nutritional index. Equipment may not be available to weigh immobile patients and for accuracy scales require regular servicing and calibration; many do not receive this (Chu et al, 1999). Shifting fluid balance with dehydration and oedema, differing scales, clothing and times of day for weighing may mean that changes do not reflect nutritional state. Weight measurement cannot differentiate muscle from fat and does not take account of overall bodily size.

Body mass index (BMI)

This is a term for weight measurements that take account of height. The most commonly used calculation is Quetelet’s Index (usually referred to as BMI) which is weight (kg) divided by height (m2). For example, someone of height 1.7m (5ft 8in) weighing 73kg has a BMI of 73/ (1.72 = 2.89) = 25.3kg/m2. Charts to look this up are available (Fig 1). There is limited consensus over cut-off values with below 20kg/m2 often regarded as suggestive of nutritional risk and less than 18kg/m2 indicative of nutritional compromise; in older people criteria may be higher (Beck and Ovesen, 1998)(e.g. less than 23kg/m2).

BMI relies upon both weight and height; height may be difficult to measure in hospital patients and misleading in older people. Knee-height and demi-span may be measured instead and different calculations applied (Bond, 1997; Chumlea et al, 1994; 1985; Bassey, 1986).

Biochemical tests

Theseare seldom used in clinical practice as they are often affected by acute illness and are then unreliable nutritional indicators (Bond, 1997). Albumin has a long half-life and is a particularly poor nutritional index, although it may indicate prognosis as it can reflect severity of illness.

Recent dietary intake

This is an important pointer towards nutritional status. Along with weight, height and recent unintentional weight loss it is one of the four basic screening questions advocated by the British Association for Parenteral and Enteral Nutrition (BAPEN; Box 4) (Lennard-Jones et al, 1995). This screening approach, using a range of methods in a composite tool, is used by most healthcare professionals.

Have you unintentionally lost weight recently?

Have you been eating less than usual?

What is your normal weight?

How tall are you?

Measure weight and height

Box4. The BAPEN 4 Questions: minimum nutritional screening

Screening tools

A large number of screening tools have been developed; selection criteria include:

Validity and reliability (Can it really differentiate those who are malnourished, at risk and adequately nourished? What patient groups is it appropriate for? Does it produce the same results if different people use it?);

User-friendliness (Is it acceptable to patients and nurses?);

Reasonable resource usage (What equipment does it need? How much training is required? How long does it take to complete?);

Sensitivity and specificity (How many people will be wrongly identified?).

A number of tools have been tested for these factors, for example the Mini Nutritional Assessment Short Form (Rubenstein et al, 2001), Nutrition Risk Score (Reilly et al, 1995) and the Malnutrition Universal Screening Tool (Elia et al, 2003) (www.bapen.org.uk/pdfs/must/must_full.pdf). The Eating Matters pack (Bond, 1997) contains more information. Many screening tools also include action plans, indicating what activities should be initiated according to different score ranges.

How often is it done?

Nutritional screening should be part of routine initial assessment procedures for all patients (Lennard-Jones, 1992; Lennard-Jones et al, 1995; Elia et al, 2003). This should be undertaken as soon as the patient’s condition allows, ideally within the first 24 hours of admission/at first contact. Monitoring is an important ongoing activity as many people experience nutritional deterioration during the course of illness and treatment. Weekly weighing is advocated as a minimum requirement with more frequent/additional activities such as keeping food record charts recommended where risk factors have been identified. Close liaison with dietitians, catering and other members of the healthcare team will help ensure that appropriate nutritional care is identified for all patients, clients and service users.

Nursing considerations

It is a multi-disciplinary responsibility to ensure that patients and clients nutritional needs are met, and nurses have particular areas of responsibility and expertise (UKCC, 1997; RCN, 2007). These occur at all levels, entailing screening, assessing, planning, implementing, evaluating and monitoring the delivery of evidence based care that meets the nutritional and hydration needs of patients, clients and users. While nutritional screening is an essential first step, other factors may also need to be considered, for example, screening swallowing function in neurological diseases including stroke (Perry, 2001; Stroke Research Unit, www.ncl.ac.uk/stroke-research-unit/coda/cointro.htm.). Nurses also have an important role in ensuring a mealtime environment conducive to eating. The Protected Mealtimes initiative (see links) is part of a UK government-supported initiative to provide better hospital food. Such initiatives reflect the importance now attached to good nutrition not just for hospital patients but as part of routine healthcare.

Appropriate and adequate nutritional support has been linked with shorter lengths of hospital stay, improvements in quality of life and cost-effective service delivery (Lennard-Jones, 1992; Green, 1999; Elia et al, 2006). Everyone benefits by ensuring that all patients, clients and service users are provided with and assisted to achieve appropriate nutritional intake.

Links

Protected Mealtimes: http://195.92.246.148/nhsestates/better_hospital_food/bhf_content/protected_mealtimes/overview.asp accessed 30.04.2007

Stroke Research Unit, QueenElizabethHospital, Gateshead. Collaborative Dysphagia Audit (CODA) Study: www.ncl.ac.uk/stroke-research-unit/coda/cointro.htm. Accessed30.04.2007.

BetterHospital Food: http://195.92.246.148/nhsestates/better_hospital_food/bhf_content/protected_mealtimes/overview.asp accessed 30.04.2007

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