Operational implications of using 2006 World Health Organization growth standards in nutrition programmes: secondary data analysis

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