Body Mass Index

Body mass index (BMI) is a quotient that has been in use since the mid-19th century. It is used to identify adults and adolescents that have an abnormal weight in proportion to their height.
It is to identify people of abnormal body mass. Clinically, the measurement is used to screen people for an excess of adipose tissue. Again, this does not directly measure adipose tissue. When people are identified with abnormal proportions, they can then be further classified based on their BMI.
When individuals are identified as an abnormal weight, certain testing should be done. For people with a BMI greater than 30 kg/m2, a lipid panel, thyroid level, and diabetes screening should always be done. These patients should be counseled about a healthy diet and exercise. For people with a BMI less than 18 kg/m2, thyroid level, comprehensive metabolic panel, psychiatric screening for an eating disorder, and conditions of malabsorption should be assessed.
These tests are considered standards of care in the American Diabetes Association Diabetes Care annual update. If their weight loss was rapid and unintentional, a cancer workup should also be done.

Related Testing

When individuals are identified as an abnormal weight, certain testing should be done. For people with a BMI greater than 30 kg/m2, a lipid panel, thyroid level, and diabetes screening should always be done. These patients should be counseled about a healthy diet and exercise. For people with a BMI less than 18 kg/m2, thyroid level, comprehensive metabolic panel, psychiatric screening for an eating disorder, and conditions of malabsorption should be assessed. These tests are considered standards of care in the American Diabetes Association Diabetes Care annual update. If their weight loss was rapid and unintentional, a cancer workup should also be done.

Clinical Significance

BMI is extremely clinically relevant. Patients should be screened for an abnormal BMI at each appointment. This is done at most clinics as part of their vital signs. For the primary care provider, an accurate BMI can help to guide your care with regards to cholesterol workup and management, diabetes screening, thyroid screening, diet/exercise counseling, and so much more. A sudden, unintentional, drop in BMI can alert the provider for more thorough cancer screenings, concern for an eating disorder, or concern for malabsorption. In other practice settings, such as surgical clinics, BMI is taken into consideration for calculating the risk of soft tissue infections and recovery time. It is important to know your patient's BMI.

Formula

BMI = weight (in kg) / height2 (in meter)

Clinical Pearls

• BMI < 18kg/m^2 is underweight.
• BMI 19-24.9 kg/m^2 is normal.
• BMI 25 - 29.9kg/m^2 is overweight.
• BMI 30 - 34.9 kg/m^2 is class I obesity.
• BMI 35 - 39.9 kg/m^2 is class II obesity.
• BMI 40 kg/m^2 and above is Class III obesity.

In the primary care setting, people should be screened for hyperlipidemia, hypothyroidism, and diabetes when they are BMI 25kg/m2 or above. They should also be counseled on diet and a exercise plans to help them lose their excess weight, and reduce their risk for co-morbidities.