There are several advantages to using BMI-for-age as a screening tool for overweight and underweight.

	BMI-for-age provides a reference for adolescents not previously available. When the 1977 NCHS growth charts were developed, weight-for-stature percentiles were provided only for prepubescent girls up to 10 years and for boys up to 11.5 years (Hamill et al., 1979). BMI-for-age is the only indicator that allows us to plot a measure of weight and stature with age on the same chart. BMI-for-age was not available in the 1977 charts. Age as well as stage of sexual maturity are highly correlated with body fatness (Daniels et al., 1997).
	BMI-for-age is the measure that is consistent with the adult index so it can be used continuously from 2 years of age to adulthood.   BMI-for-age is not recommended for use in the United States before 2 years of age to screen for growth. BMI values at young ages have a weak association with adolescent or adult obesity (Whitaker et al., 1997; Guo et al., 1994).
	BMI can be used to track body size throughout the life cycle. This is important because BMI-for-age in childhood is a determinant of adulthood BMI. For more about the tracking of BMI:

  BMI-for-age relates to health risks.

  BMI-for-age correlates with clinical risk factors for cardiovascular disease including hyperlipidemia, elevated insulin and high blood pressure. Freedman and colleagues used data from the Bogalusa Heart Study and found that approximately 60% of 5- to 10-year-old children who were overweight had at least one biochemical or clinical risk factor for cardiovascular disease such as those just mentioned, and 20% had two or more risk factors (Freedman et al., 1999).

  BMI-for-age during pubescence is related to lipid and lipoprotein levels and blood pressure in middle age (Must et al., 1992). Risk factors in children can become chronic diseases in adults.

BMI-for-age compares well with both weight-for-stature measurements and measures of body fat.

  A study completed by researchers at the CDC (Mei et al., 2002) compared the performance of BMI-for-age and weight-for-stature with fatness measured by dual energy x-ray absorptiometry (DXA), a direct measure of adiposity.

  NHANES III data were used to test how well BMI-for-age predicts underweight (below the 15th percentile) and overweight (above the 85th percentile) relative to the traditional weight-for-stature in children 2 to 19 years old.

  Both BMI-for-age and weight-for-stature performed equally well in screening for underweight and overweight among children 3 to 5 years of age.

  For school-aged children (6 to 11 and 12 to 19 age groups), BMI-for-age was slightly better than weight-for-stature in predicting underweight and overweight.

  Ratios of weight relative to stature such as BMI-for-age and weight-for-stature may be used as indirect measures of overweight that correlate with direct measures.

  CDC recommends the use of BMI-for-age for children aged 2 years and older. However, weight-for-stature performs equally well in preschool aged children and can be used in this age group.

  BMI-for-age is significantly correlated with subcutaneous and total body fatness in adolescents (Barlow and Dietz, 1998).