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Using nutritional screening tools to identify malnourished patients

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Identifying malnourished or ‘at risk’ patients is not always easy, this article looks at the the correct use of nutritional screening tools

Lin Perry, PhD, MSc, RGN, RNT is Senior Research Fellow, Newcastle Institute of Public Health, University of Newcastle, New South Wales.

Why do we need screening tools?

Many acutely or chronically unwell people experience dietary difficulties and deficiencies related to or resulting from their illness. Nutritional screening aims to identify those who are malnourished or ‘at risk’ of becoming so (Bond, 1997). There are a wide variety of signs and symptoms of nutritional problems. Keeping a record of what is eaten may be useful but accurate records can be difficult and time-consuming. Body measurements and biochemical tests can be used but many are difficult to undertake with bed-bound or disabled people and are affected by disease. No single test is adequate. To address this problem composite screening tools have been developed, and a bewildering array is available.

In the UK the British Association for Parenteral and Enteral Nutrition (BAPEN) has long been concerned at the difficulties posed for healthcare professionals by the number of tools available, the limited work undertaken to demonstrate whether they are ‘fit for purpose’, and by the frequent omission of nutritional screening when patients first contact health services. This is important as screening is an essential first step in the management of patients’ nutritional care (Powell-Tuck, 2007; NCCAC, 2006; Better Hospital Food, 2001).

Choosing a tool

It is essential to ensure that the tool chosen has demonstrated its merits, is ‘fit for purpose’ and that appropriate agreements are in place before it is implemented. For example, how accurate is it likely to be across the wide range of patient groups seen in most hospitals? Who will carry out screening? Who will provide training to use the tool? How will referrals be made to obtain full assessment by a dietitian? If care is transferred from one organisation to another, such as when a patient moves from hospital to community care, will other healthcare professionals understand what the screening results show?

The Malnutrition Advisory Group of BAPEN tackled these issues by developing the Malnutrition Universal Screening Tool (MUST), which is increasingly being adopted by UK healthcare providers (Torodovic et al, 2003; Elia, 2003). However, when deciding which tool to use, a first consideration is the range and variety of people to be screened. Is one tool to be used hospital or community-wide or is the target an individual patient group, for example, older people in residential care? The tool needs to have demonstrated its merits with the appropriate patient group. Criteria for choice of screening tools have been identified (Box 1).

Box 1. Criteria for choosing a tool (Cochrane and Holland, 1971)

  • Ability to give a true measure of a patient’s degree of ‘risk’ (validity)

  • Ability to give consistent results when used by different people (reliability)

  • Ease of use and intelligibility to those carrying out the screening

  • Acceptability to patients

  • Acceptability in terms of resource usage, such as time and equipment

  • Sensitivity - ability to detect ‘risk’ when really present

  • Specificity - ability to produce negative results where the patient is not ‘at risk’.

The tool must be able to distinguish those who are well-nourished from those malnourished or at risk of becoming so (the validity of the tool). This may be judged by various means, such as by asking the opinion of a group of experts (‘face’ validity, the most basic approach), comparing it with results of other reputable nutritional measurements (‘concurrent’ validity), seeing whether it is able to predict nutrition-related outcomes (‘predictive’ validity).

Accuracy is important, considering how well the tool performs in detecting people who really have problems and correctly identifying those who do not (sensitivity and specificity).

Reliability is also essential as the tool must produce similar results with repeat testing in the same circumstances and with different users where the patient’s state has not changed. User-group may affect tool performance; for example, whether doctors, nurses or dietitians conducted the screening.

Those carrying out the screening must find the tool easy to use and it must be acceptable to those being screened. Finally, resources are a consideration: is extensive training required, how long does it take to complete and does it need additional equipment?

What tools are available?

Full analysis and referencing of all tools available is beyond the scope of this but further detail is available (Jones, 2002; Bond, 1997). Table 1 sets out characteristics of commonly used tools developed for hospital-wide application and use with older adults. Tables 2 and 3 outline the work that demonstrates validity and reliability of these tools. As these tables demonstrate, the tools that have undergone most study are Mini Nutritional Assessment (MNA) and MUST; however, for screening purposes a Short Form of MNA has been developed. To date there has been limited study of MNA-SF beyond correlation with MNA.

Click here for Table 1: Characteristics of selected screening tools

Click here for Table 2. Validity of nutrition risk screening tools

Click here for Table 3. Reliability of nutrition risk screening tools

How should screening tools be used?

All patients should be screened at first contact with a healthcare professional, on admission to hospital and for outpatients at their first clinic appointment. Screening should be repeated weekly for inpatients and when there is clinical concern for outpatients. People in care homes should be screened on admission and when there is clinical concern. Hospital departments who identify groups of patients with low risk of malnutrition may opt out of screening these groups. Opt-out decisions should follow an explicit process via the local clinical governance structure involving experts in nutrition support (NCCAC, 2006).

Results of this preliminary investigation will indicate next steps. Many screening tools and the UK NICE guidelines (NCCAC, 2006) include an ‘action plan’; for example, referral for full nutritional assessment by a dietitian where the tool indicates malnourishment or high risk; monitoring and review of weight/dietary intake for those identified as ‘at risk’. Some screening tools are suitable for repeated use as monitoring tools. The possibility of deterioration and need for re-screening should always be born in mind, even when patients appear initially well-nourished.


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