What is the BMI for Underweight?

Appeared in: NORCET 2 - 2021 (shift-1)

Explanation

According to the World Health Organization (WHO), a Body Mass Index (BMI) of less than 18.5 kg/m² is classified as underweight.
BMI is a standard screening tool calculated by dividing a person's weight in kilograms by the square of their height in meters (kg/m²).
Being underweight can indicate malnutrition and is associated with health risks like a weakened immune system, osteoporosis, and anemia.

Visual 1: Infographic - A color-coded chart showing the different BMI categories from underweight to severe obesity with their corresponding numerical ranges. This provides a quick visual reference for the classifications.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Body Mass Index (BMI) classification for adults as background academic context rather than a clinical decision trigger.
Nurses routinely calculate BMI as part of the initial patient assessment to screen for nutritional risks (both undernutrition and obesity), which can impact recovery, wound healing, and medication metabolism.
A low BMI should prompt the nurse to perform a more detailed nutritional assessment, inquire about diet, and consider a referral to a dietitian.
What if? If a patient has a very high muscle mass (e.g., a bodybuilder), their BMI might fall into the 'overweight' or 'obese' category despite having low body fat. In such cases, BMI is a less reliable indicator of health risk, and other measures like waist circumference or skinfold thickness are more appropriate.

How to Approach the Question

This is a factual recall question that tests your knowledge of a standard clinical classification.
First, identify the key term in the question: 'BMI for Underweight'.
Recall the standard WHO BMI categories that are used in clinical practice.
Compare the recalled value for the 'Underweight' category with the given options.
Select the option that correctly matches the definition, which is a BMI of less than 18.5.

Concept Tested & Keywords

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Practise the full NORCET 2 - 2021 (shift-1)

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