Body mass index

Why does the patient’s/client’s body mass index need to be calculated?

First, we need to know what ‘body mass index’ is.

A body mass index – or ‘BMI’, as you’re more likely to hear it called – is a formula that allows us to measure how appropriate a patient’s/client’s weight is for his or her height, gender and age. Scientists have been able to use BMI to work out appropriate weight ranges – in other words, they can say what a healthy weight is for a man who is, for instance, 40 years old and 1.8 metres in height. Different ranges have been developed for men, women and children.

Calculating a patient’s/client’s BMI is important because we know that scores that lie outside the normal range for height, gender and age can be associated with health problems.

When should I check it?

This will depend very much on why the patient/client is needing to access health services. If he or she is on a weight-gain or weight-reduction programme in hospital or a care home, the weight and BMI may initially be calculated weekly, although it may be every fortnight or even monthly in community settings. Other patients/clients, such as those who have just started drugs (diuretics) to help them to lose excess fluid from their bodies, may need to be weighed daily in the early days to see how effectively fluid is being lost (again, the frequency will be less in the community). The times to check the weight and BMI will be set out in the patient’s/client’s care plan.

How do I check it?

Luckily, we don’t have to get our papers, pens and calculators out to estimate BMIs, as there are charts which do the calculation for us.

Have a look at our animation on how to calculate a BMI.

What do my findings mean?

The World Health Organization has defined the normal ranges for BMI which, for adults, are:

  • normal: 18.5 to 24.9
  • underweight: less than 18.5
  • severe underweight:less than 16
  • overweight: greater than 25
  • obese: greater than 30

Those whose BMI is too high (that is, they are too heavy for their height, gender and age) may be at risk of the diseases associated with overweight and obesity (such as heart disease, joint diseases, diabetes and cancer). Those whose BMI is too low may be suffering from malnutrition or may even have a psychological illness such as anorexia or bulimia.

Where should I record and report my findings?

The patient/client will have a chart on which weight and BMI can be recorded. You should make sure you record your findings clearly and accurately so that they can be readily seen and understood. If you find the weight or BMI has changed (either increasing or decreasing) by more than a couple of points since the last recording, you must report it to the registered person in charge. Always follow your organisation’s policies and procedures on recording and reporting.

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