BMI (Body Mass Index)
A weight-for-height ratio used to screen for weight categories
Definition
Body Mass Index (BMI) is calculated as weight in kilograms divided by height in meters squared (kg/m²). It is a widely used screening tool for underweight, normal weight, overweight, and obesity categories.
Categories (Adults)
- Underweight: Less than 18.5
- Normal: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obese Class I: 30 to 34.9
- Obese Class II: 35 to 39.9
- Obese Class III (extreme): ≥40
Limitations
BMI does not distinguish lean muscle mass from fat. Athletes may fall into overweight categories despite low body fat. It is also less accurate in pregnancy, edema, elderly, and children (use BMI-for-age percentile).
Nursing Applications
Calculate BMI on admission as part of nutritional screening. Counsel on healthy eating, physical activity, and refer to dietitian for extremes. Consider waist circumference as adjunct risk measure.
NCLEX Relevance
Know normal BMI range (18.5 to 24.9) and that BMI ≥ 30 defines obesity. Tested in health promotion and nutrition content.