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fechar este livroAssessment of Nutritional Status in Emergency-Affected Populations - Adolescents (UNSSCN, 2000, 24 p.)
fechar esta pastaPossible solutions for the future
Ver o documento(introduction...)
Ver o documentoChanges in body proportions with age
Ver o documentoPubertal development
Ver o documentoInter-ethnic differences in genetic growth potential
Ver o documentoUse of other data

(introduction...)

No single method has proved adequate for assessment of undernutrition in adolescents in emergency situations. Below are listed some possible strategies for overcoming the major difficulties.

Changes in body proportions with age

An anthropometric index that is unrelated to age is required if adolescents do not know their ages. The Rohrer Index may offer such advantages over weight-for-height, BMI, or MUAC. Further research is required in this area.

Pubertal development

Simpler methods of determining pubertal stage may, in the future, allow adjustment for this complicating factor. Such methods could include appropriate line drawings or photographs of different Tanner stages. In contrast, it may be easier and more accurate when assessing adolescents to consider pre-pubertal and post-pubertal adolescents separately. Ideally, this would require the assessment of the presence or absence of only one landmark of sexual development, rather than the determination of different levels of a development indicator, such as Tanner breast or genital stages. Such separation may make it possible to include pre-pubertal adolescents with school age children and post-pubertal adolescents with adults when choosing which anthropometric indicator or cut-off point to use.

Inter-ethnic differences in genetic growth potential

A method has been proposed to account for at least part of the difference in body shape in adults by calculating a BMI which is adjusted for the Cormic Index 75-77. However, this procedure remains untested in adolescents (Nicholas Norgan, personal communication). Theoretically, such an adjustment could also be applied to other anthropometric indices calculated from weight and height, such as weight-for-height or the Rohrer Index. The application of this technique to adolescents may be complicated by the normal changes in Cormic Index throughout adolescence. Moreover, some data indicate that chronic undernutrition changes the Cormic Index 78. Stunted children may have a greater Cormic Index than comparable children without stunting.

An additional method of compensating for ethnic differences would be to choose different, more appropriate cut-off points (either % of median or z-scores) to define undernutrition when using a reference population whose ethnicity differs from that of the survey population. Some populations may be genetically thinner than the reference population, requiring a lower cut-off to define undernutrition. WHO recommends such a procedure when using anthropometry to screen persons for admission to nutritional rehabilitation 12. Nonetheless, the procedure of determining appropriate cut-off points is not simple. Such a process would require either data on health outcomes in order to estimate a functional cut-off or data on a well-nourished population of similar ethnicity in order to derive a statistically-defined cut-off point. Collection of such data for multiple ethnic groups would be expensive and time-consuming.

Using a local reference would permit comparison of a survey population to well-nourished adolescents of the same ethnicity. Although this has been used in published surveys 79, creation of a reference population is a difficult task requiring substantial resources. Separate reference populations cannot be created for each nationality or ethnicity. An alternate possibility would be to create a few reference populations for use with major ethnic categories. Investigators could then choose a reference which most closely matches the survey population. For example, if a survey population is known to have an average Cormic Index of 0.50, the investigators would use a reference population with a similar average Cormic Index. Of course, such a strategy would make comparison of the results of different surveys very difficult if they used different reference populations to calculate the prevalence of undernutrition. In addition, it would require measuring sitting height as well as standing height in all surveys of adolescents.

A single, international reference population consisting of adolescents from multiple countries could be used, similar to that currently under development for children less than 5 years of age. A reference population described in recently published work includes children and adolescents from national surveys done in six countries 80. In this proposal, cut-off points for BMI to define overweight and obesity were identified by determining the centile among 18 year-old adolescents in each national survey population which matched the adult BMI cut-off points of 25 and 30. That centile was then applied separately for males and females to each one-half year age group from 2-17.5 years to determine the cut-off BMI value at for each age and sex group. The cutoff points for each national population were then averaged to produce age- and sex-specific cut-off points for the combined international reference. The same procedure could be used to determine cut-off points which correspond to the adult cut-off points for various degrees of undernutrition, i.e., BMI of 16, 17, and 18.5 kg m-2. This proposed reference and the method of determining cut-off points for BMI eliminates the bias which may result from using as a reference a sample from a relatively obese population, such as American adolescents. However, its use still requires accurate ages because the BMI cut-offs change substantially with age, and it does not correct for differing ages of sexual maturation. In addition, the reference proposed may not be appropriate for populations with different body shape, such as Nilotic Africans and Australian aborigines.

Use of other data

When assessing adolescents, additional data from the same population should be collected. Such data could include the prevalence of undernutrition in young children, the prevalence of undernutrition in adults, rates of morbidity and mortality, and information on food security, food distribution, and alternate sources of food. If a survey of adolescents indicates substantial undernutrition, but data on young children, adults, and other population groups do not demonstrate undernutrition or elevated morbidity or mortality, it is very important to look critically at the adolescent data. It is unlikely that adolescents are the only population group with substantial undernutrition.

Unless anthropometric measures are valid, i.e., they truly measure nutrition and health, they may not be useful at all. Other measures, such as strength or other functional outcomes, may better reflect an individual's risk of nutrition-related morbidity or mortality. Experience in screening adults for admission to therapeutic feeding programmes has demonstrated that three clinical signs (apparent dehydration, oedema, and inability to stand) predict mortality better than BMI 59, 63. Such an approach, although as yet untested in adolescents, may be able to distinguish adolescents in need of therapeutic feeding from those who could benefit from a less intensive feeding program. However, clinical signs may not be useful for measuring the overall prevalence of lesser degrees of undernutrition in a population because persons with less severe undernutrition may not be so markedly impaired nor exhibit such a distinctive clinical picture.

Measures of muscle function, such as grip strength, shuttle run, or maximum jump height, may be able to detect moderate degrees of wasting. One author proposes that muscle performance may actually be affected earlier in the course of undernutrition than body composition 81. In one study among surgical patients, hand grip was associated with MUAC, and those patients with hand grip less than 85% of normal did much poorer postoperatively 82. In a second study, muscle strength, as measured by grip strength, endurance run, shuttle run, distance throw, and standing long jump, was greater in normally-nourished children 4-6.5 years of age than undernourished children 83. However, in this study, muscle strength was correlated with stature, and after removing the effect of this variable, well-nourished and poorly-nourished children no longer differed in muscle strength. A third study that directly stimulated the ulnar nerve and measured isometric muscle contractions did not find a difference between undernourished and normally nourished adults 84. Clearly, such measures are not ready to be used in the field. Much more work needs to be done to determine whether appropriate measures of muscle function exist, to describe a reference population and cut-off points, and to determine the sensitivity and specificity of proposed methods to detect moderate and severe undernutrition.