How to calculate a MUST score: the malnutrition universal screening tool, step by step

To calculate a MUST score, work out three separate scores and add them together: a BMI score (0, 1 or 2), an unplanned weight-loss score for the last three to six months (0, 1 or 2), and an acute disease effect score (0 or 2). A total of 0 means low risk, 1 means medium risk, and 2 or more means high risk. The arithmetic takes a minute. The value is in doing it every month, on the same scales, and acting on the result.

The short answer

MUST stands for Malnutrition Universal Screening Tool. It was developed by BAPEN, the British Association for Parenteral and Enteral Nutrition, and it is the screening tool used across the NHS and in almost every UK care home. Step 1 is the BMI score: over 20 scores 0, 18.5 to 20 scores 1, under 18.5 scores 2. Step 2 is the weight-loss score: unplanned loss of under 5 per cent in three to six months scores 0, 5 to 10 per cent scores 1, over 10 per cent scores 2. Step 3 is the acute disease effect score: 2 if the person is acutely ill and has had, or is likely to have, no nutritional intake for more than five days, otherwise 0. Step 4 adds them. Step 5 is the action: low risk means routine care and repeat monthly; medium means observe with a food chart and repeat; high means treat, refer and review. The rest of this guide takes each step slowly, including what to do when you cannot get a weight or a height.

What is a MUST score and why does it matter in a care home?

Malnutrition is common in care homes, it is often missed, and it makes almost everything else worse: pressure ulcers, falls, infections, wound healing, mood, confusion. A person who is losing weight without meaning to is telling you something is wrong, and MUST is the structured way of noticing before it becomes a crisis.

The tool is universal because it is designed for any adult in any setting: hospital, community, care home. It is a screen, not a diagnosis. A high score does not tell you why the person is losing weight; it tells you to find out. The what does MUST stand for question comes up in every induction, and the answer is worth more than the letters: it is a monthly check that the person in front of you is eating enough to stay well.

CQC expects care homes to screen for malnutrition and act on the result under the safe and effective key questions, and NICE clinical guideline CG32 on nutrition support recommends screening on admission and at regular intervals. In a care home, regular means monthly, and more often where there is concern.

At a glance: the three steps and the scores

Before you start: weigh and measure properly

The score is only as good as the weight. Weigh the person on the same scales, at the same time of day, in similar clothing, without shoes, every month. Record the date, the weight, the scales used and anything unusual, such as a plaster cast or a full bladder. Calibrate the scales at least yearly and after any move.

Chair scales and hoist scales are fine as long as the same ones are used each time. If the person cannot be weighed on any scales, use the alternative measurements below and record which one was used. Do not estimate a weight by eye and do not carry forward last month's weight as if it were new. A blank is more honest than a guess.

Height only needs to be measured once, unless the person is young enough to still be growing or has a condition that changes it. Measure it standing if possible; if not, use ulna length.

Step 1: the BMI score

BMI is weight in kilograms divided by height in metres squared. A person of 62kg and 1.62m has a BMI of 62 divided by 2.62, which is 23.6. Score it: over 20 is 0, 18.5 to 20 is 1, under 18.5 is 2.

Two things trip people up. The first is units: use kilograms and metres, not stones and centimetres. The second is the boundary: exactly 20 scores 1 on the BAPEN chart, and 18.5 scores 1. The BAPEN MUST calculator and the printed chart both do this for you, and a health monitoring record that calculates BMI and the MUST score from the weight removes the arithmetic altogether.

A BMI over 30 scores 0 on MUST but it is not nothing. Obesity is a health concern in its own right and should be in the care plan. And a person with a high BMI can still be malnourished; that is what step 2 is for.

Alternative measurements when height cannot be taken

If the person cannot stand, or has a spinal curvature, measure ulna length: from the point of the elbow to the midpoint of the prominent bone of the wrist, on the left arm if possible, with the arm bent across the chest. Read the estimated height from the BAPEN table, which differs for men and women and for under and over 65. Record that ulna length was used.

If neither weight nor height can be obtained, measure mid upper arm circumference at the midpoint between the shoulder and the elbow, on the left arm. A MUAC under 23.5cm suggests a BMI under 20; over 32cm suggests a BMI over 30. It gives a category, not a number, and it is a last resort, but it is far better than no screen at all.

Step 2: the unplanned weight-loss score

This is the step that catches people the BMI misses, and it is the step most often skipped because nobody can find the old weight. Compare the current weight with the weight three to six months ago. Subtract to get the loss, divide by the previous weight, multiply by 100. A person who was 68kg and is now 62kg has lost 6kg, which is 6 divided by 68, which is 8.8 per cent.

Score it: under 5 per cent is 0, 5 to 10 per cent is 1, over 10 per cent is 2. Unplanned is the key word. Someone who has lost weight on purpose with a dietitian's support does not score. Someone who has lost weight without trying does.

If there is no weight from three to six months ago, you cannot score this step properly. Score it 0 for now, write clearly that the weight-loss score is unknown, weigh the person today, and repeat the screen next month with a real comparison. Admission is the moment to ask: the hospital discharge summary, the GP record or the family may have a weight from earlier in the year.

Getting the percentage right

Divide by the previous weight, not the current one. 6kg lost from 68kg is 8.8 per cent. 6kg divided by the current 62kg would give 9.7 per cent, which is wrong and could push someone across a threshold. The BAPEN weight-loss tables do the calculation for you if you prefer to look it up.

Step 3: the acute disease effect score

This scores 2 if the person is acutely ill and there has been, or is likely to be, no nutritional intake for more than five days. Otherwise it scores 0. There is no score of 1.

In a care home this is uncommon. It applies to someone who is seriously unwell, post-operative, or with a severe infection, and who is not eating at all. It does not apply to someone who is eating less than usual, or who has missed a couple of meals, or who has a cold. Scoring it for reduced appetite is the commonest error in step 3 and it inflates the total.

If someone genuinely meets this criterion in a care home, the MUST score is the least of the concerns. They need a clinical review that day.

Step 4: add the scores and find the risk level

Add the three numbers. 0 is low risk. 1 is medium risk. 2 or more is high risk. A MUST score 2 is high risk whichever steps it came from: a BMI under 18.5 alone, or 5 per cent weight loss plus a BMI of 19, or acute disease alone.

Write the total and the risk level on the screening record with the date and the three component scores, not just the total. The components are what tell the reviewer what is going on. A score of 2 from BMI alone in someone who has always been slight is a different picture from a score of 2 from a 12 per cent weight loss in someone who was a healthy weight.

Step 5: the action at each risk level

The score is worthless without the action. BAPEN's management guidelines set out what to do at each level and every care home should have them written into its nutrition policy.

Whatever the score, treat any underlying cause: mouth pain, poorly fitting dentures, swallowing difficulty, constipation, depression, medication side effects, or simply food the person does not like.

Worked example one: Margaret, medium risk from weight loss

Margaret is 84 and lives in a residential home. On admission six months ago she weighed 68kg. Today she weighs 62kg. Her height is 1.62m. She has a chest infection but is still eating small meals.

1. BMI. 62 divided by (1.62 x 1.62) = 62 divided by 2.62 = 23.6. Over 20, so the BMI score is 0.
2. Weight loss. 6kg lost. 6 divided by 68, times 100, is 8.8 per cent. Between 5 and 10 per cent, so the weight-loss score is 1.
3. Acute disease. She has an infection but she is eating. Score 0.
4. Total. 0 + 1 + 0 = 1. Medium risk.

If you only looked at BMI you would miss Margaret. Her BMI is fine. It is the unplanned weight loss that puts her at medium risk. The action is a three-day food and fluid chart, a note in the care plan, a check of her dentures and her mouth, a repeat weight in a month, and a conversation with the GP if the chart shows she is eating poorly.

Worked example two: David, high risk from BMI alone

David is 41, has a learning disability, and lives in a supported home. He weighs 52kg and is 1.75m. He has always been slim. There is a weight from four months ago of 53kg. He is well.

1. BMI. 52 divided by (1.75 x 1.75) = 52 divided by 3.06 = 17.0. Under 18.5, so the BMI score is 2.
2. Weight loss. 1kg lost. 1 divided by 53, times 100, is 1.9 per cent. Under 5 per cent, so the weight-loss score is 0.
3. Acute disease. He is well. Score 0.
4. Total. 2 + 0 + 0 = 2. High risk.

David is high risk on BMI alone, even though his weight is stable. That is correct: a BMI of 17 means he has very little reserve, and any illness could tip him quickly. The action is referral to the dietitian, a look at what he eats and why he eats little, a care plan goal around weight gain if he wants it, weekly weights, and a review with the GP. His stable weight is reassuring but it does not reduce the score.

How often to screen in a care home

Screen on admission, within the first week, and then monthly. Screen again whenever there is concern: a visible change in the person, clothes becoming loose, a period of illness, a change in swallowing, a bereavement, a change in mood. Screen weekly for anyone at high risk until the dietitian advises otherwise.

Monthly is the minimum, and it only works if the weights are monthly too. A screen with no new weight is not a screen. The most reliable arrangement is a fixed weighing day, say the first Monday of the month, with one person responsible for making sure every resident is weighed, the weights entered, and the scores calculated the same day.

Recording MUST: what the record needs to show

For each screening, record the date, the weight, the scales, the height or the alternative measurement used, the BMI, the previous weight and its date, the percentage loss, the three component scores, the total, the risk level, the action taken and the name of the person who did it. Keep a running series so the trend is visible at a glance.

On paper that is a weight chart per person with columns for each of those items. On a digital record, the weight is entered and the BMI, the percentage change and the score are calculated, with the trend shown as a line. Either way, the care plan should reference the current score and the action, and the review should check the two agree. Kiwi calculates BMI and the MUST score from each monthly weight and shows the trend, which is the kind of evidence trail the audit below relies on. The nutrition and fluid chart guide covers the food and fluid records that follow a medium or high score.

Linking MUST to the care plan

A MUST score is not an end in itself. A medium or high score changes the care plan: the eating and drinking section records the score, the cause if known, the goal, the plan (fortified food, snacks, supplements, texture changes, help at mealtimes, a different table, a different time), the monitoring, and who is involved. The daily log records meals against that plan. The review compares the log with the plan and the next weight with the last.

Where the score falls again, record why: the infection resolved, the dentures were fixed, the new menu worked. That is the evidence that the home noticed, acted, and the action worked, and it is exactly what an inspector wants to see. The care plan guide covers the eating and drinking section in detail.

MUST and pressure ulcer risk

Nutrition is one of the main factors in pressure ulcer risk, and the Waterlow score includes it. A rising MUST score should prompt a look at the Waterlow score, and vice versa. A person who scores high on both needs a coordinated plan: nutrition support, pressure relief, skin checks, and a review of mobility and continence, because the same underlying illness is usually driving all of them. The Waterlow guide explains how the two tools fit together.

Doing both on the same weighing day, with the same weight, is the efficient arrangement. It also makes the link visible: a person whose MUST has gone from 0 to 1 and whose Waterlow has gone from 12 to 16 in the same month has one problem, not two, and the plan should say so. Skin checks recorded on a body map in the daily log alongside the food chart give the reviewer the whole picture without opening three folders.

MUST in learning disability and mental health services

The tool is the same but the challenges differ. People with learning disabilities may have lifelong low or high BMI, swallowing difficulties, food selectivity, or medication that affects appetite, and the screen needs to be read against their baseline. A person who has had a BMI of 17 for twenty years still scores 2, and still needs a dietitian's view, but the plan will be about maintaining rather than reversing.

In mental health services, weight change is often a sign of the illness or a side effect of the medicine. Antipsychotics commonly cause weight gain; depression and some other conditions cause loss. A MUST score that changes is a prompt for a medicines review as well as a nutrition plan. Consent and capacity apply: a person with capacity may decline supplements or weighing, and that is recorded and respected, with the risk explained and the offer repeated.

Using a MUST calculator

BAPEN publishes a free online MUST calculator and printable charts, and most care management systems build the calculation into the health monitoring record. A calculator removes arithmetic errors, which are common, particularly in the percentage step. It does not remove the need for an accurate weight, a real previous weight, and a sensible judgement on the acute disease step.

If you use a calculator, check that it is using the BAPEN thresholds and that it is being fed the right numbers. A calculator given last month's weight because nobody weighed the person this month will produce a confident and wrong result.

The monthly MUST procedure

1. On the fixed weighing day, weigh every resident on their usual scales, at the usual time, in similar clothing, and record the weight and the scales.
2. For anyone who cannot be weighed, take the alternative measurement and record which one was used.
3. Enter the weight and calculate BMI, or let the system do it.
4. Find the weight from three to six months ago and calculate the percentage loss, or record that no comparison is available.
5. Decide the acute disease score honestly: only 2 if there is no intake for more than five days.
6. Add the scores, record the components and the total, and record the risk level.
7. Take the action for the level: routine, food chart, or referral.
8. Update the care plan for anyone at medium or high risk, and note the score for everyone.
9. Flag anyone whose score has risen since last month to the manager the same day.
10. Record who did the screening and when, and check at the end of the day that nobody was missed.

The MUST audit checklist

• Every resident has a weight recorded this month, or a documented reason and an alternative measurement.
• Every resident has a MUST score this month with the three components shown.
• Every weight-loss score has a previous weight and date behind it, or is marked unknown.
• No acute disease score of 2 has been given for reduced appetite.
• Every medium-risk score has a three-day food and fluid chart that was completed and reviewed.
• Every high-risk score has a referral, a care plan update and weekly weights.
• Every score that rose since last month was flagged and acted on.
• The scales have been calibrated in the last year.

Keep the audit with the screening records, dated and signed, with the actions and when they were closed. If you would like to see how the weighing day, the automatic scoring and the audit fit together in one record, book a demo.

Common mistakes

• Scoring BMI only. Weight loss is the most sensitive step and the one most often skipped because nobody can find the old weight.
• Not weighing monthly. Without a series of weights, step 2 is impossible.
• Dividing by the wrong number. Divide by the previous weight, not the current one.
• Scoring acute disease for eating less. It is for no intake for more than five days, not for a poor appetite.
• Carrying forward an old weight. The score looks complete and is fiction.
• Recording the score and doing nothing. A score of 2 with no referral is worse than no score, because it shows the home knew.
• Different scales each month. A 2kg difference between two sets of scales looks like 3 per cent weight loss.
• Ignoring the other direction. A BMI over 30 scores 0 but still belongs in the care plan.

What good looks like on inspection day

The inspector asks how the home monitors nutrition. The manager shows the weighing day, the weight chart for a resident with twelve monthly weights on the same scales, the MUST score each month with its three components, and the trend line. They pick a resident whose score rose from 0 to 1 in June. The record shows the three-day food chart, the note that she was struggling with her dentures, the dental appointment, the softer menu, and the score back to 0 in August with her weight recovering.

They pick a resident at high risk. The record shows the dietitian referral within the week, the fortified diet plan, the supplements prescribed, weekly weights, and a care plan that says all of it. They ask a care worker what a MUST score is and the worker says it is the monthly check that people are not losing weight without meaning to, and that a 2 means the dietitian.

That is inspection-ready evidence: not that nobody lost weight, but that every loss was seen, scored, explained and acted on, and the record shows all four.

Final conclusion

A MUST score is three simple numbers added together, and the arithmetic is the easy part. The hard part is the discipline: the same scales every month, a real previous weight, an honest acute disease score, and an action that matches the level. Screen on admission and monthly, record the components and not just the total, put the score and the plan in the care record, and follow the trend. Do that and the tool does what it was built for: it finds the person who is quietly slipping, months before anyone would otherwise notice.

Frequently asked

What does MUST stand for?

Malnutrition Universal Screening Tool. It was developed by BAPEN, the British Association for Parenteral and Enteral Nutrition, and is the standard screen for malnutrition risk in UK hospitals, community services and care homes. It is a screen for risk, not a diagnosis.

How do you calculate a MUST score?

Add three scores. BMI: over 20 is 0, 18.5 to 20 is 1, under 18.5 is 2. Unplanned weight loss over three to six months: under 5 per cent is 0, 5 to 10 per cent is 1, over 10 per cent is 2. Acute disease: 2 if the person is acutely ill and has had or will have no intake for more than five days, otherwise 0. Total 0 is low risk, 1 medium, 2 or more high.

What is step 1 of MUST?

Step 1 is the BMI score. Calculate BMI as weight in kilograms divided by height in metres squared, then score it: over 20 scores 0, 18.5 to 20 scores 1, under 18.5 scores 2. If height cannot be measured, use ulna length from the BAPEN table; if neither weight nor height can be obtained, use mid upper arm circumference to estimate the BMI category.

What does a MUST score of 2 mean?

A MUST score of 2 or more is high risk. The action is to treat: refer to a dietitian or nutrition support team unless no benefit is expected, set goals, improve intake with fortified food and supplements if advised, weigh weekly, update the care plan and review with the GP. A score of 2 from BMI alone in someone whose weight is stable still counts as high risk.

How do you calculate the MUST weight-loss score?

Subtract the current weight from the weight three to six months ago, divide by the previous weight, and multiply by 100. Under 5 per cent scores 0, 5 to 10 per cent scores 1, over 10 per cent scores 2. Only unplanned loss counts. If there is no previous weight, score 0, mark it unknown, and repeat next month with a real comparison.

How often should MUST be done in a care home?

On admission within the first week, then monthly, and again whenever there is concern such as loose clothing, illness, a change in swallowing or mood. Weekly for anyone at high risk until the dietitian advises otherwise. Monthly screening only works if the person is weighed monthly on the same scales.

Is there a free MUST calculator?

Yes. BAPEN publishes a free online MUST calculator and printable charts including the BMI, weight-loss and ulna length tables. Many care management systems also calculate BMI and the MUST score automatically from the monthly weight. A calculator removes arithmetic errors but still depends on an accurate weight and a real previous weight.

Sources

• BAPEN: MUST calculator and explanatory booklet
• BAPEN: The MUST report, nutritional screening of adults
• NICE clinical guideline CG32 Nutrition support for adults
• CQC: guidance on meeting nutritional and hydration needs, Regulation 14
• NHS England: Guidance on nutrition and hydration in care homes
• Skills for Care: Care Certificate standard 8 fluids and nutrition