Can someone tell me in more details about the usefulness of MUAC for height? Can this be used in children > 5yrs to identify SAM?
There is a reference for MUAC/H here. This extends to 145 cm in height.
Using a reference such as this selects cases based on position with regard to parameters of a reference distribution. References are usually designed to reflect normal growth or, in the case of the WHO references, ideal growth
An indicator designed to represent ideal growth may not be ideal for the purpose of identifying children, or populations, requiring emergency nutrition interventions. The primary aim of most anthropometric surveys is to identify populations in need of emergency nutrition interventions. The primary aim of interventions treating acute malnutrition is to prevent mortality. In this context, the most useful case-definition will be one that can identify individuals who are at high risk of dying if they remain untreated but would be likely to survive if treated in an appropriate nutrition support program. This realisation has led a number of workers to argue that the utility of case-definitions for malnutrition are defined more by their ability to reflect mortality risk than than their ability to reflect ideal growth. Studies examining the prognostic or predictive value (i.e. of predicting death) of various anthropometric indicators in young (i.e. aged 6 - 59 months) children have consistently reported that MUAC uncorrected for height or age and using a fixed threshold to perform better than all other practicable indicators. This is the basis for using a single MUAC threshold for children aged between 6 and 59 months.
It is likely that a similar approach will be useful for older children. The problem then is finding a case-defining threshold for older children. This is not easy. There are ethical and practical issues. The ethical issue is that, with the development of effective treatment protocols for SAM and therapeutic products such as RUTF, we really cannot deny treatment to thin, sick, and weak children with clinical signs of wasting such as visible severe wasting, recent rapid weight loss, "baggy-pants", and very thin arms and legs. This means that we cannot stand by and watch to see who lives and who dies without treatment as we did with the historical cohorts. The practical issues are that, outside of specific clinical populations, wasting is very rare in children aged 6 - 10 years and death is also rare in this age group (i.e. compared to younger children). This means following a very large population over a very long time. This is a very expensive thing to do.
I think that "SAM" in this age-group in the general population is very rare. I am a little reluctant to even call it "SAM". It strikes me that the children you are interested in will have TB, HIV, or some other clinical condition. We might call this "secondary malnutrition". If these cases are already in treatment then they should be picked up through weight monitoring at clinic visits (with children this will be like growth monitoring as a child should gain weight). If these cases are new to care then treatment should include nutritional rehabilitation. It seems to me that MUAC/H might have a role here. We could use (e.g.) a two-stage screening approach with MUAC/H z-score < -2 followed by a clinical / laboratory screen. The exact MUAC/H threshold used would be calibrated to achieve good sensitivity at high specificity.
You may also want to ask this question on EN-NET.