Rapid Responses to:

RESEARCH: Andrew Seal and Marko Kerac Operational implications of using 2006 World Health Organization growth standards in nutrition programmes: secondary data analysis BMJ 2007; 334: 733 [Abstract] [Full text]

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On the WHO Child Growth Standards

Mercedes de Onis, Adelheid W. Onyango   (15 March 2007)

Reply from the authors

Andrew J Seal, Marko Kerac   (5 April 2007)

On the WHO Child Growth Standards 15 March 2007
Mercedes de Onis, Coordinator World Health Organization, Adelheid W. Onyango Send response to journal: Re: On the WHO Child Growth Standards	The paper by Seal and Kerac has prompted queries from concerned users of the software World Health Organization (WHO) Anthro 2005. The paper states that "the available software for the WHO growth standards (WHO Anthro 2005) fail to distinguish between children with wasting and those with oedema" (page 2) and that "the program fails to separate cases with oedema and account for them as a separate category of severe malnutrition in its summary statistics....this may have the effect of falsely reducing the reported prevalence of nutritional oedema" (page 5). Both these statements are incorrect. The software WHO Anthro 2005 does include cases with oedema in the prevalence of cases classified as wasted (<-2 standard deviation (SD) weight-for-height) and severely wasted (<-3 SD weight-for-height), making it consistent with standard reporting systems. In addition, it reports the number of cases in the data set that had oedema. Further the paper presents an analysis of the WHO Child Growth Standards that is incorrect both from a conceptual and an epidemiological point of view. The authors have manipulated the WHO standards to recreate weight-for-height reference values in a way that does not respect the methodology used to construct the original standards. The use of the percent-of-median classification is inappropriate because it ignores the inherent skewness of weight-based indicators. Therefore, the newly created values cannot any longer be referred to as the "WHO standards". With the newly created values (misleadingly still referred to as the "WHO standards") the authors proceed to do an inappropriate comparison of the original WHO z-score values (to derive prevalences of severe malnutrition) with their newly derived "WHO values" in percent-of-median (to screen individual children for selective feeding programmes). The authors conclude that the two applications of the standards do not yield consistent results and describe this as paradoxical. Indeed, different results are to be expected as two different sets of values (i.e. the original WHO values and the values derived by the authors) and two different classification systems (ie, z-scores and percent-of-median) are used in the comparison. The paper has other inaccurate statements. For example, it equates - 2SD with 80% of median and -3SD with 70% of median. These cut-offs classify children differently and those working in nutrition programmes are familiar with the problems this entails. Furthermore, the authors state that percent-of-median is a widely used tool in nutrition programmes. As shown by a global survey on growth monitoring practices (1) only 6% of national programmes use the percent-of-median classification system compared with 63% using percentiles and 18% using z-scores. As a matter of fact none of the existing growth references have presented percent-of-median reference values. In sum, it is regrettable that the paper will likely add more confusion than clarity to a field that is in need of clear concepts. 1. de Onis M, Wijnhoven TMA, Onyango AW. Worldwide practices in child growth monitoring. J Pediatr 2004;144:461-5. Competing interests: We coordinate the WHO Child Growth Standards project.
Reply from the authors 5 April 2007
Andrew J Seal, Lectuer in International Nutrition UCL Centre for International Health and Development, Marko Kerac Send response to journal: Re: Reply from the authors	We welcome the rapid response from de Onis and Onyango and agree that it is important to minimise any confusion in this field. It is for this reason exactly we have written our paper. By identifying potential problems due to inappropriate use of new WHO growth Standards at this early stage, many difficulties can be addressed and unintended consequences avoided before large scale roll-out. The rapid response raises two main issues that we would like to address. (1) WHO Anthro 2005 We stand by our concerns over the reporting format used by WHO Anthro 2005. The main standard case definitions for reporting the prevalence of acute malnutrition when using z-scores are: - Acute Malnutrition (commonly referred to as Global Acute Malnutrition (GAM)): <-2 z-scores weight-for-height or nutritional oedema - Moderate Acute Malnutrition: -3 to <-2 Z scores weight-for- height - Severe Acute Malnutrition (SAM): <-3 z-scores weight-for-height or nutritional oedema These definitions have important practical implications. Malnutrition programme managers and policy makers make decisions on the basis of accurately and clearly stated levels of GAM and SAM. In addition, though there are overlaps and similarities, Kwashiorkor (oedematous malnutrition) and marasmus (wasting malnutrition) are clinically and pathophysiologically distinct entities and this needs to be recognised and reported. Unfortunately, WHO Anthro 2005 does not currently report the prevalence of oedematous malnutrition and in situations where there is a high prevalence of oedema the reported prevalence of wasting may be misleading. This is because the software adds together children with nutritional oedema or wasting and, instead of labelling then as acutely malnourished, classifies them simply as wasted (<-2 SD Weight for length/height) and/or severely wasted (<-3 SD Weight for length/height). From the standard case definitions given above it follows that children may be suffering from SAM but have a weight-for-height >=-3 z- scores on account of their oedema. Children may also be suffering from GAM but have a weight-for-height >=-2 z-scores (also on account of their oedema). The WHO Anthro results output is therefore potentially misleading because children with oedema are placed in the <-2 or <-3 z-score categories when they may not actually have such a weight-for- height. The results output does include a footnote stating that cases with oedema are included in the <-2 and <-3 z-score categories and gives the number of cases with oedema. However, to ensure correct and easy reporting the data needs to be disaggregated and separate prevalence figures given with associated confidence intervals. (2) General approach used in the paper Turning to the second more general point from de Onis and Onyango that "the paper presents an analysis of the WHO Child Growth Standards that is incorrect both from a conceptual and an epidemiological point of view". The paper unashamedly addresses the issue from a pragmatic and operational position, i.e. what might happen if and when people start to use the new growth standards as a replacement for the current NCHS reference. We are in fact well aware of the statistical and conceptual issues around Z/SD scores vs. % of median. But what may be obvious to academics and high-level policy makers may not be so obvious to those on the ground. Therefore, in our opinion, the appropriate analysis from a conceptual and epidemiological perspective was to look at what would happen if people applied the current case definitions for selective feeding (based on percentage of the median and recommended in current WHO publications) in conjunction with the newly released standards. While the paper quoted by de Onis and Onyango (de Onis et al., 2004) in their rapid response looked at the use of anthropometric indices in growth monitoring, our paper looked at the use of anthropometry in selective feeding programmes. Therefore, although the finding that percent of the median is used in 6% of national growth monitoring programmes is interesting, it is of limited relevance to the current discussion. As stated above, we agree with de Onis and Onyango that this is an area in need of clarity. This is especially true given the global use of anthropometry as an assessment tool and the large numbers of children affected by the resulting targeting decisions. To this end we suggest that WHO should be prepared to consider whether a review of the case definitions used in WHO Anthro 2005 is required. The gaps that exist in our knowledge of how to use the WHO Growth Standards for the diagnosis of malnutrition in developing countries are real and serious. However, this situation should not be viewed just as a threat but also as an opportunity. Using the research evidence currently being compiled, the nutrition community may be able to move towards an integrated assessment tool for acute malnutrition that meets the need for needs assessment and clinical admissions. We look forward to further constructive dialogue, both with WHO, and other key stakeholders on these important issues. (1) Management of severe malnutrition: a manual for physicians and other senior health workers. WHO (1999), p.4 Competing interests: Authors of the paper