|Assessment of Nutritional Status in Emergency-Affected Populations - Adolescents (UNSSCN, 2000, 24 p.)|
The World Health Organization (WHO) currently recommends using the BMI (Body Mass Index) of individual adolescents compared to a reference population made up of adolescents in the United States and using the 5th centile of this reference as the cut-off point to define undernutrition. These recommendations may not be appropriate; surveys using these recommendations have found unrealistically high levels of adolescent undernutrition.
PROBLEMS WITH ANTHROPOMETRY IN ADOLESCENTS
Anthropometry may be more difficult in adolescents than other age groups because of many complicating factors.
Body proportions, including indices using weight and height measurements, change with age, making it necessary to compare an individual to adolescents in a reference population who are of the same age. As a result, age must be collected on persons screened for admission to feeding programs or measured as survey subjects. Adolescents in many emergency affected populations do not accurately know their ages.
Body proportions change with sexual development. The age at which sexual development occurs differs in different populations and complicates the comparison of subjects from one population to adolescents in a reference population.
Body proportions may differ between the reference and survey populations. It may not be valid to expect all populations of adolescents, even if well nourished, to achieve the same body proportions as a single, universal reference.
These problems affect all anthropometric indices including weight-for-height, BMI, Rohrer Index (weight/height3), and MUAC (mid-upper arm circumference). Regardless of the anthropometric index used, the following adjustments may allow better estimates:
Better methods of assessing the age of attainment of key pubertal landmarks may allow adjustment for differences in maturation age between survey and reference populations.
Cormic Index (sitting height/standing height ratio) may, to some extent, be used to adjust for ethnic differences in body proportions; however, this technique has not been studied in adolescents.
A new international reference consisting of adolescents from 6 countries and a new method of determining cut-off points may alleviate some of the biases from using a reference population from a single country.
Additional research is necessary before a single, valid methodology can be widely recommended for anthropometric assessment of adolescents. Only tentative and preliminary recommendations can be given at this time.
Until better methods can be developed and validated, screening for severe undernutrition in order to determine the need for therapeutic feeding should use clinical criteria.
In surveys, some correction for different ages of sexual maturation should be carried out if the age of sexual maturation differs substantially between the survey and reference population:
For pre-pubertal adolescents, weight-for-height could be used as the anthropometric index and compared to revised weight-for-height tables currently in use.
For post-pubertal adolescents, BMI could be used as the anthropometric index and compared to a new international reference population. Appropriate cut-off points could be used to identify malnourished individuals.
Regardless of which index is used, cut-off points are age-specifc; as a result, age should be collected as accurately as possible on all adolescents measured during screening or survey activities.
The reference population of American adolescents, currently recommended by WHO for use with BMI, should not be used.
Adolescents should not undergo nutritional assessment in isolation. Young children, women of childbearing age, adults, elderly, or other population subgroups should also be assessed. A large discrepancy between the estimated level of undernutrition in adolescents and other population subgroups should stimulate investigation of the validity of the methods and results of the adolescent assessment. Estimates of the levels of morbidity and mortality, and information on diet, food security, and food sources should also be collected
In order to assess the methods and comparability of surveys, all survey reports should describe in detail the anthropometric index used, how measurements were taken, which reference population was used, how individuals were compared to this reference, the cut-off points used to define various degrees of undernutrition, and any other ancillary data collected on the population of interest.
Signalling the need for norms and standards.
The SCN will identify for the attention of technical agencies or other bodies critical areas where norms and standards are missing or out-of-date and holding programmes back. This includes (especially) identifying knowledge gaps and significant areas in dispute or controversy; as well as identifying areas requiring operational research, and facilitating this work.
Extract from the ACC/SCN's Strategic Plan, April 2000