12. Plotting and interpreting BMI-for-age using the English system

A Case Study of ‘Sam’

Step 1. Obtain accurate weights and height measurements

Date of Birth (DOB): 9/15/94

Date of Visit (DOV): 4/4/98

Weight: 37 pounds 4 ounces

Height: 41 1/2 inches

Step 2. Select the appropriate growth chart

Because Sam is a normal 3.5 years old, a standing height was obtained. The appropriate chart to use is the ‘Boys 2 to 20 BMI-for-age’ chart.

Step 3. Record the data

On the data entry table found on the clinical growth chart, information relevant to the growth chart is recorded. Here data has been recorded for the date of visit, the child’s age, weight and height at the visit.

Step 4. Calculate BMI

Calculate BMI at the time of the clinic visit.

Calculations:

Convert ounces and fractions to decimals:

Weight of 37 lbs and 4oz = 37.25 lbs (16 ounces = 1 pound so 4oz/12 oz = 0.25).

Height = 41.5 in.

BMI: (37.25 lbs/41.5 in/41.5 in) x 703 = 15.2

Then the BMI of 15.2 is entered on the data entry table.

Step 5. Plot measurements

All the necessary information is recorded and Sam’s BMI can be plotted. On the BMI-for-age chart, find Sam’s age on the horizontal axis and visually draw a vertical line up from that point. Then find his BMI on the vertical axis and visually draw a horizontal line across from that point. The point where the two intersect represents Sam’s BMI-for-age.

When plotted on the growth chart, Sam’s BMI-for-age falls just below the 25th percentile curve.

Step 6. Interpret the plotted measurements

Since Sam’s BMI-for-age falls just below the 25th percentile curve, this means that of 100 children with the same gender and age as Sam, fewer than 25 children have a BMI lower than his. Sam is neither overweight, underweight nor at risk of overweight.

When a child’s plotted measurement falls between the 5th and 85th percentiles it is considered to be in the normal range. Sam’s BMI-for-age is in the normal range based on this measurement.