Dear fellow nutritionists,
I have read the various previous questions regarding the question on how to assess adolescent malnutrition, including the literature (For example: Woodruff + Duffield 2000 as well as the recent Save the Children review of SUN+ countries in 2015). I have also looked through the WHO website for the growth references etc. However, we are still faced with a dilemma in which I would like input from this fantastic group on.
In line with the Save the Children review, we also face difficulties on using BMI-for-age as currently seems to be the recommendation. The reasons this review state also hold true (impact of growth retardation, individual process of maturation) but the most difficult one is actually age identification. In many contexts, age is difficult enough to determine for the 6-59month category, let alone for a 14 year old!
I have seen that there has been a recent shift in the recent national protocols - previously it used to be weight-for-height for adolescents, but now more and more in updated protocols I am seeing BMI-for-age, which poses a rather big challenge in implementation. I would love to understand more in detail the reasoning behind this (I do understand that the WHO Growth standards data was better etc) and how to deal with the repercussions in implementation with poor age-knowledge. Is there something very wrong about weight-for-height in adolescents that I am not gathering? Why is it that BMI-for-age appears to be the main method of assessment for adolescents now - has there been something new that I have missed? And...could anyone else share some experiences of using these two methodologies?
As always, thanks for all the great input and ideas that this forum brings.
Hello Anonymous 502
Weight-for-height was never used to assess the anthropometric status of adolescents using the old WHO/NCHS growth references, it was only applied to girls <10y and boys <11.5 y.
Weight-for-age was applied to all children up to the age of 18 y, but in the new WHO growth references it is only applied to children up to the age of 10 y.
The only indices that are now calculated for all children from birth to 19 y (228 months) are height-for-age and BMI-for-age. BMI-for-age is the only index that incorporates body weight, but it is greatly complicated by the fact that BMI is expressed as kg/m2 and the z-score is based on values of BMI for children by sex and month of age. Weight-for-age and BMI-for-age are hard to compare. You can find a comparison of the NCHS and new WHO growth references for older children and adolescents in the American Journal of Clinical Nutrition, 2011, 94:571.
The new WHO growth references for children from 5 - 19 y published in 2007 were based on the old NCHS data treated using new statistical methods, they were not based on new data for this age group. The curves of the index of BMI-for-age were adjusted statistically so that a z-score of BMI-for-age of +1 roughly meets at 19 y with a BMI of 25 for adults, who are classified as overweight, and a z-score of BMI-for-age of +2 roughly meets at 19 y with a BMI of 30 for adults, who are classified as obese. The intention in designing the new reference curves was, I think, that BMI-for-age and BMI converge at 19y and BMI-for-age is the index of overweight for children. BMI alone should only be used to assess overweight in adults. BMI and BMI-for-age both suffer from issues related to body shape and muscularity rather than just adiposity, so they need to be treated with caution as a basis for judging overweight.
This means that different indices of overweight and underweight are used for children of different ages: weight-for-height for children <5 y and BMI-for-age for children from 5-19 y.
No index for age will be useful if age is wrong. We found evidence in Ethiopia that when children were enrolled in primary school their age was set to the official age at entry, 7 y, probably because children were 'grown' enough to be enrolled in school. There is also evidence from surveys that children who are stunted enrol late in school, so have a negative age-for-grade score: a child enrolled in the right grade at the right age has a score of zero; a child who is 1 year late has a score of -1, and so on. There may be a negative correlation between age-for-grade score and z-score of height-for-age (see Social Science and Medicine, 1999, 48: 675).
Answered:
6 years agoHi Andrew,
Thanks for your rather prompt and detailed reply.
I used to see weight for height percentile tables for adolescents which I know a few organisations used to use and which I know are in some protocols - for example in the Central African one I have and I know in a few others. This I think has risen from the exact problem you mentioned - without age, we can't use an index which includes it.
In a way this was my question - the recommended one is using the BMI-for-age and now WHO has changed their website and some national protocols (such as in South Sudan) and everything to this, however, it is not applicable in the field at all. Age even for 7 year olds as you mention is fraught with problems, so by the age of 14 the room for error is so large.
I know there are few organisations working with adolescents but I was wondering what others are doing when working with them. Is weight-for-height really so bad? Is there recent research on MUAC for height cut-offs? I know there has been various pieces of ad hoc work on this and would like to find out more.
Thanks as always for the input,
Answered:
6 years ago