Body Mass Index (BMI)

Function

Body Mass Index (BMI) is a surrogate marker for body fatness based on an individual's mass (weight) and height. While it does not measure body fat directly, research has shown that BMI is moderately correlated with more direct measures of body fat obtained from skinfold thickness measurements, bioelectrical impedance, underwater weighing, and dual-energy X-ray absorptiometry (DXA).

Why it is Ordered

BMI is used as a screening tool to identify possible weight problems for adults. However, BMI is not a diagnostic tool. For example, a person may have a high BMI but to determine if excess weight is a health risk, a healthcare provider would need to perform further assessments. These assessments might include skinfold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings.

Associated Conditions

BMI is widely used to categorize health status and predict risks for several chronic conditions.

• High BMI (Overweight/Obese): Associated with an increased risk of Type 2 Diabetes, Hypertension (high blood pressure), Dyslipidemia, Coronary Heart Disease, Stroke, Osteoarthritis, and certain cancers (endometrial, breast, and colon).
• Low BMI (Underweight): Associated with risk for osteoporosis, decreased immune function, iron-deficiency anemia, and malnutrition.

Clinical Limitations

It is important to note that BMI does not distinguish between muscle mass and fat mass. Athletes or individuals with high muscle mass may have a BMI that classifies them as 'overweight' despite having very low body fat. Conversely, older adults who have lost muscle mass may fall into a 'normal' BMI range while possessing high levels of visceral fat.