As demonstrated in this study, analyses of relative proportions of SAM and MAM cases identified by MUAC vs. WHZ criteria in the community is critical in the investigation of the expected consequences of an “expanded MUAC-only” programming scenario on targeting. Through our secondary analysis of a large number of cross-sectional surveys, we identified two important potential drawbacks of the “expanded MUAC-only” scenario.
First, our analyses demonstrates substantial decrease in the number of targeted SAM children, as compared with the population of children who are severely acutely malnourished and eligible for rehabilitative nutrition programs. A switch to “expanded MUAC-only” programs would lead to situations where a large proportion of SAM children and families in need would be denied access to these services. Of critical concern is the fate of the 50% SAM children, at high risk of death, who would be deemed ineligible for treatment or receive sub-standard treatment under an “expanded MUAC-only” scenario. In addition, about 50% of MAM children in the community would also be excluded a priori from these programs. The first drawback to expect is thus a large a priori restriction of the coverage of SAM and MAM cases.
Second, our results show a seemingly counterintuitive (given reduction in target discussed above) increase of the number of children who would be eligible to receive RUTF as part of their treatment. This is the result of a change in the population eligible for RUTF-based treatment, from the current target population (all SAM children) to all children with MUAC< 125 mm. SAM children would constitute approximately one-third of this “new target” population and the rest (around 70%) would be comprised of MAM children. Even though a lower RUTF dosage is intended for MAM cases under this scenario, still a large part of the RUTF-related costs, from purchase to end-user distribution will be allocated to MAM children. Considering the current situation where RUTF-related costs, which constitute a large proportion of therapeutic feeding program costs, are one of the key barriers for the scaling-up of these therapeutic feeding programs and their sustainability [13, 33], the universal expansion of RUTF use for MAM children would be a programmatic challenge. Since this expansion would occur at the same time as RUTF is denied or restricted for many SAM children, the planned increase in the level of support for MAM children may ultimately take place at the expense of SAM children. The second drawback to expect is thus a potentially inequitable use of the costly RUTF resource, outside its initial (and principal) indication.
It has been argued that SAM children presenting with a WHZ < -3 but a MUAC> = 115 mm are relatively healthy, and that SAM children with a low MUAC have a higher risk of death [22, 34]. These hypotheses are being challenged by a range of clinical studies [35, 36], as well as by direct observation of mortality risks in cohorts of patients  and in large community cohorts . It appears that the initially formulated hypothesis that SAM children with low WHZ are at lower mortality risk than low MUAC SAM children was driven by analyses affected by Simpson’s paradox, comparing populations of cases not appropriately disaggregated . The recent evidence suggests that SAM children with low WHZ and those with low MUAC have similar risk of death [3, 20]. This evidence also shows that children presenting with both deficits (low MUAC and low WHZ) or with combined low WHZ and oedema display much higher risk of mortality than children with only one deficit (low WHZ or low MUAC). Arguing in favor of the prioritization of these small subpopulations of SAM cases with both deficits or with combined low WHZ and oedema seems justified, especially in situations of dramatically constrained resources, such as sudden RUTF shortages or at the onset of an acute crisis. The identification and adequate treatment of this subpopulation of SAM cases in such exceptional resource-restricted situations would require the measurement of WHZ alongside MUAC and oedema. Although “expanded MUAC-only” programs would include this subpopulation of SAM children, these children would remain unidentified (since WHZ is not measured), and their specific elevated risks would go unaddressed. Further, under “expanded MUAC-only” programs, these children may be discharged early, without reaching the minimal WHZ level indicative of recovery .
Besides simple exclusion, the “expanded MUAC-only” program would also classify a large part of the population of SAM cases as MAM. The expected consequence of this would be to treat them with a lower RUTF dose, without routine medical treatment, and with a lesser level of medical assessment and follow-up, which may affect treatment outcomes Although currently available evidence on this topic is limited, a RUTF dose meeting total daily nutritional requirements may improve recovery and prevent relapse compared to RUTF given as a supplement to the usual diet . Recent studies involving uncomplicated SAM patients reported important incidence of co-morbidities and referrals to hospital during the treatment period, thereby highlighting the importance of keeping these patients under close medical attention [39, 40]. Failure to adequately address co-morbidities occurring during outpatient treatment has been highlighted as important risk factors of poor treatment outcomes . Accordingly, randomized controlled trials comparing treatment outcomes with or without systematic antibiotic treatment showed that this component of SAM outpatient therapeutic feeding protocols is also required to prevent medical complications and deaths during treatment [8, 36, 42, 43]. As summarized by Bhutta and colleagues, all components of care are required to ensure optimal treatment outcomes, beyond the choice of food commodity . Therefore, adverse consequences on treatment outcomes can be expected when SAM cases are misclassified, underestimated, and subsequently undertreated as MAM.
It is difficult to provide relevant estimations of the negative consequences of excluding 50% of the MAM caseload, i.e. those children with WHZ < -2 and MUAC≥125 mm. Both the exact levels of morbidity and mortality risk, the physiological needs of MAM children, as well as the best way to promote their recovery, are not well established [15, 44]. However, these MAM children who would be excluded from “expanded MUAC-only” programs represent the bulk of the United Nation agencies’ joint estimates of global wasting caseload, since only WHZ < -2 indicator is used to produce these estimates .
The basic demographic profile of the SAM and MAM children show that while the majority of those included in the MUAC-only program would be young (< 2 years) children and females, about 30% of the children excluded from treatment would be younger than 2 years and about 40% would be female. This is in line with what we know about the usual distribution of age and sex in the population of children with a MUAC below an absolute cut-off, as compared with the population of children with a low WHZ and a MUAC above the cut-off [6, 46]. The clinical significance of this difference in age and sex between excluded and included SAM and MAM children is not straightforward. On the one hand, it has been argued that younger children and girls have a higher risk of death among malnourished children and that the proportion of cases with these characteristics would further indicate that low MUAC children are more at risk than the other SAM children . On the other hand, it has long been demonstrated that young children and girls have lower MUAC values than older children and boys because they are smaller, and this alone does not necessarily signify the higher mortality risk. This rather means that a lower level of anthropometric deficits is required for them to fall under an absolute MUAC cut-off than for older children and boys . While this explains the higher proportion of young children and girls among children classified as SAM or MAM according to an absolute MUAC value, it may also indicate lower levels of nutritional impairments and lower associated risk of death in these subcategories of low MUAC SAM children. A recent analysis of mortality risks associated with anthropometric deficits further confirmed this hypothesis by showing a lower increase in the risk of death associated with MUAC< 115 mm in young children than in older children . In that study, sex did not appear to have a role in the mortality risk associated with anthropometric deficits.
Of note, the difference in prevalence of wasting as assessed by WHZ versus the prevalence assessed by MUAC is greatest in crises when wasting by WHZ becomes more prevalent . Drawbacks of the MUAC-only approach resulting in an underestimation of caseload and exclusion of those in need of treatment are thus expected to worsen in crisis, as confirmed by the field experiences in crises and higher caseload contexts . Therefore, the higher the prevalence of wasting in the population (indicating a crisis), the higher proportion of MAM and SAM children will remain undetected by a MUAC-only program.
The rationale for the expansion of the use of RUTF to MAM children also warrants further discussion. Although positive impacts of lipid-based nutritional supplements on MAM recovery and weight gain have been reported in the past , considerable knowledge gaps remain. Of note, WHO recently recommended not to provide any nutritional products as a supplement for MAM children outside of exceptional circumstances . First, it is unclear what the optimal requirements for MAM children are, and second, it is very likely that there would be options other than RUTF to adequately improve their diet [15, 50]. It has been proposed for instance that programmatic solutions relying on the improvement in complementary foods and child health through a more holistic approach would achieve similar results in the short term and better ones in the mid to long term. Concerns have also been raised about potentially deleterious impact of product-based approaches relying on high-fat and high-sugar processed foods at a time when the double burden of under- and overnutrition is increasingly threatening the health of low and middle income country populations .
The increase in the targeted number of children cannot be easily translated in terms of increase in quantity of RUTF, given the number of parameters which have to be taken into account but either remain unresolved (appropriate RUTF dosage for MAM, duration of treatment) or may be highly context-dependent (changes in coverage, logistical costs associated with RUTF supply and distribution). However, a large increase in RUTF-related costs (not only for purchase but also for transport and distribution) is likely to accompany the two- to three-fold increase in numbers of children eligible for RUTF support. Concerns have been raised about the use of RUTF outside its initial target, the conflicts of interests which may arise in this growing market, and opportunity cost of not directing resources for potentially better long-term investments [52,53,54]. Expanding the use of RUTF for the purpose of program simplification may provide additional arguments to this criticism.
There is no doubt that adoption of an “expanded MUAC-only” program scenario would lead to dramatic simplification of the current normative guidance for management of acute malnutrition and would address many of the barriers faced by program implementers and Ministries of Health in resource constrained environments. However, the potential limitations of targeting demonstrated in this study as well as potential consequences for coverage, effectiveness and cost-effectiveness of such programs may preclude others for considering such simplified approach outside of exceptional circumstances, where WHZ measurement for screening, admission and discharge purposes is simply not feasible. In such circumstances, “expanded MUAC-only” programs could be considered as a temporary option. Effectiveness and cost-effectiveness of this approach in exceptional circumstances should be further investigated and might ultimately be considered as inadequate.
A major strength of this study is the high number and quality of the cross-sectional surveys it builds upon. The 550 surveys contributing to the analysis are almost all surveys conducted by Action Against Hunger during the recent period 2007–2018. During these surveys, planning, data collection and analysis followed standardized methods embedding rigorous quality controls  and were supervised and validated a posteriori by highly qualified and trained staff. These surveys focused on countries where acute malnutrition is likely a problem and where feeding programs are implemented, including emergency contexts. This study however has several limitations. First, only 22 countries (those for which we had 5 or more surveys) were included. The disaggregation of the results by country and region is thus for illustration; these data cannot be considered as representative globally or regionally. Furthermore, surveys were mostly of small scale, with the objective of providing an accurate estimate of wasting at the district level. Thus, the results we obtained may not be representative of the country overall. We also demonstrate that large variability exists within countries and regions, so one cannot readily predict at the lower administrative level where we should expect more excluded children. Considering potential biases, it is important to mention that countries with more surveys have more influence on the regional or global estimates – for example, about 30% of included surveys are from DRC. In DRC, low MUAC or oedema detect higher proportions of SAM and MAM children compared with other regions. Considering that countries where these proportions are on the contrary very low, such as India or Bangladesh, contribute only 1.6 and 6.7% of the surveys we analyzed, while they are major contributors to the global caseload for acute malnutrition, the global consequences of the “expanded MUAC-only” program scenario on the exclusion or underestimation of acute malnutrition cases is likely underestimated.