Using Body Mass Index with Children and Teens?

 

Body Mass Index is a screening tool that is used to identify children with possible weight problems. CDC and the American Academy of Pediatrics (AAP) recommend the use of BMI to screen for overweight and obesity in children beginning at 2 years old.

BMI is not a diagnostic tool but is used to screen children for obesity, overweight, healthy weight, or underweight. For example, a child may have a high BMI for age and sex, but in order to determine if excess fat is a problem, a health care professional 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.

How is BMI calculated and interpreted for children and teens?
Calculating and interpreting Body Mass Index using the BMI Percentile Calculator involves the following steps:

1. Before calculating BMI, obtain accurate height and weight measurements.

2. Calculate the BMI and percentile using the Child and Teen BMI Calculator. The Body Mass Index number is calculated using standard formulas.

3. Review the calculated BMI-for-age percentile and results. The BMI-for-age percentile is used to interpret the BMI number because BMI is both age-and sex-specific for children and teens. These criteria are different from those used to interpret BMI for adults — which do not take into account age or sex. Age and sex are considered for children and teens for two reasons:

The amount of body fat changes with age so the Body Mass Index for children and teens is often referred to as BMI-for-age.

The amount of body fat differs between girls and boys.

The CDC BMI-for-age growth charts for girls and boys take into account these differences and allow translation of a Body Mass Index number into a percentile for a child’s or teen’s sex and age.

4. Find the weight status category for the calculated BMI-for-age percentile as shown in the following table.

Underweight - Less than the 5th percentile.

Healthy weight - 5th percentile to less than the 85th percentile.

Overweight - 85th to less than the 95th percentile.

Obese - Equal to or greater than the 95th percentile.

Source: Centers for Disease Control and Prevention

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What is Body mass Index?

Body Mass Index (also known as BMI) is a number calculated from a child’s weight and height. BMI is a reliable indicator of body fatness for most children and teens. BMI is not an exact measurment of body fat, but research has shown that it does correlate to direct measures of body fat. BMI can be considered an alternative for direct measures of body fat. BMI is also an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.

For children and teens, BMI is age and sex specific and is often referred to as BMI-for-age.

What is a BMI percentile?

After BMI is calculated for children and teens, the BMI number is plotted on the CDC BMI-for-age growth charts (for either girls or boys) to obtain a percentile ranking. Percentiles are the most commonly used indicator to assess the size and growth patterns of individual children in the United States. The percentile indicates the relative position of the child’s BMI number among children of the same sex and age. The growth charts show the weight status categories used with children and teens (underweight, healthy weight, overweight, and obese).

BMI-for-age weight status categories and the corresponding percentiles are shown below.

Underweight - Less than the 5th percentile

Healthy weight - 5th percentile to less than the 85th percentile

Overweight - 85th to less than the 95th percentile

Obese - Equal to or greater than the 95th percentile

Source: Centers for Disease Control and Prevention