Malnutrition - Diagnosis 

Diagnosing malnutrition 

Several things are taken into account to check if you are malnourished or if you are at a high risk of malnutrition.

In adults, these include:

  • your body mass index (BMI), which is a measure that can determine if you are a healthy weight for your height 
  • whether you have unintentionally lost weight in recent months
  • whether an illness means you are unable to feed yourself or absorb nutrients from your diet

You would normally be considered malnourished if you have a BMI of less than 18.5 or you have unintentionally lost more than 5-10% of your body weight during the last three to six months. However, in some cases doctors may be concerned about malnutrition if you have a BMI below 20.

You may be considered at a high risk of malnutrition if:

  • an illness means you have eaten nothing or almost nothing for the last five days or are likely to eat nothing or almost nothing for at least five days
  • you do not absorb nutrients from food well, for example you have a condition such as Crohn’s disease that is causing inflammation inside your digestive system
  • there is an underlying reason why your body is likely to use up nutrients at a higher rate or have an increased need for nutrients
  • you have difficulty eating and drinking

A vitamin or mineral deficiency can normally be diagnosed with a blood test.

Diagnosing malnutrition in children

Diagnosing malnutrition in children involves taking a measurement of their weight and height and then comparing it against what would be the expected average height and weight for a child of that age.

Some children will be below average as they are naturally smaller, but a significant drop below the expected level for an individual could indicate a risk of malnutrition.

Blood tests can also be used to measure levels of protein in the blood. Low levels of protein may suggest that a child is malnourished.


Page last reviewed: 04/02/2013

Next review due: 04/02/2015

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Recognising malnourishment

The National Institute for Health and Care Excellence (NICE) recommends that healthcare professionals should look for signs of malnutrition when:

  • you register at a GP surgery
  • you attend a routine check-up or hospital appointment
  • you are admitted to hospital or a care home

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Get advice on how to cope if your child has an eating disorder, including what to expect and dealing with mealtimes