Malnutrition Screening: the method, the errors, and the exam

What the skill is for

Malnutrition screening exists to catch nutritional risk before it becomes nutritional harm. A patient can look well nourished and still be losing ground fast, particularly after a fracture, a bowel resection, or a chest infection that has kept them off food for four days. The screen is not a diagnosis. It is a filter that sorts patients into low, medium, and high risk so that the ones who need a dietitian actually get one.

The tool most wards use, commonly a version of MUST (Malnutrition Universal Screening Tool), works from three questions: how much unintentional weight has the patient lost recently, what is their current BMI, and is there an acute disease effect meaning they have had or will have no nutritional intake for more than five days. Each answer scores 0 to 2, and the total predicts outcome. Higher scores correlate with longer length of stay, delayed wound healing, and higher readmission risk. That predictive value is the reason the screen is done on every admission, not just for patients who look thin.

The method, step by step

Start with weight history. Ask the patient directly whether they have lost weight without trying, over roughly the last three to six months, and how much. If they cannot say, check old notes, GP letters, or ask a family member. Unintentional loss of more than 5% of body weight scores 1; more than 10% scores 2.

Calculate BMI from current height and weight. Under 18.5 kg/m2 scores 2, 18.5 to 20 kg/m2 scores 1, above 20 scores 0. Weigh the patient yourself where possible rather than relying on a stated figure, since self-reported weight is frequently inaccurate in either direction.

Assess acute disease effect. This asks whether the patient is acutely unwell and has had, or is likely to have, no nutritional intake for more than five days. A patient nil by mouth pending surgery, or one with severe pancreatitis, scores 2 here regardless of their weight or BMI. Add the three scores together. Zero is low risk, one is medium risk, two or more is high risk, and each band has a defined care pathway: routine monitoring, food record charts and review, or dietitian referral with a nutritional care plan.

Where it goes wrong

The most common error is skipping the weight history question because the patient looks an average size, and scoring only on BMI. A patient with a BMI of 24 who has lost three stone in two months is still high risk, and BMI alone would miss it entirely. The weight loss question exists precisely to catch this group.

The second error is estimating rather than measuring. Stated height and weight, or a visual guess, introduces enough error to shift a patient between risk bands. Where a patient cannot stand to be weighed, use documented alternatives such as ulna length or mid-upper arm circumference rather than omitting the measurement.

The third error is treating the score as static. A patient screened as low risk on admission can become high risk five days later if they have been kept nil by mouth for a procedure that was postponed twice. Rescreening on a set schedule, and after any change in clinical status, is part of the skill, not an optional extra.

Practising it deliberately

Run the three questions against real admission scenarios rather than memorising the scoring table in isolation. Take a case: a 78-year-old admitted with a hip fracture, BMI 19.2, reports losing weight over the past two months but cannot quantify it precisely. Practise deciding what counts as sufficient evidence of unintentional loss and how to score when the patient's own account is vague.

Build fluency in the acute disease effect question specifically, since it is the one most often forgotten. Practise flagging it for patients who are nil by mouth, ventilated, or awaiting bowel surgery, even when their admission weight and BMI look unremarkable.

Practise the handoff as much as the scoring. Knowing a patient scored high risk is only useful if you can state what happens next: dietitian referral, food record chart, and a defined review point. Rehearse saying that sentence out loud until it is automatic.

Applying it on the exam

NCLEX items on malnutrition screening usually present a scenario and ask which finding most increases risk, or which action the nurse should take first. Expect the test to bury the relevant weight loss or intake history in a paragraph of other data, testing whether you can extract it rather than whether you know the scoring table by name.

Questions may also test prioritisation: given several patients, which should be referred for nutritional assessment first. The answer is usually the patient combining two risk factors, such as low BMI plus five days of no oral intake, over a patient with only one factor present.

Watch for distractor options built on assumption rather than data, such as assuming a patient is malnourished because they are elderly, or assuming they are not because their BMI is normal. The correct answer follows the three-question method, not appearance or age.

A worked example

A 65-year-old is admitted with a bowel obstruction and is made nil by mouth pending possible surgery, expected to remain so for at least six days. His BMI is 22.4, and he reports no recent weight loss. Weight loss scores 0, BMI scores 0, but acute disease effect scores 2 because of the anticipated five-plus days without intake. Total score is 2, placing him in the high-risk category despite a normal BMI and no weight history.

The correct nursing action is dietitian referral and initiation of a nutritional care plan, which may include consideration of parenteral or enteral feeding if surgery or oral intake is delayed further. A nurse who screens only on BMI would miss this patient entirely, since 22.4 sits comfortably within normal range. The case illustrates why all three elements of the tool must be applied, not just the one that is quickest to calculate.