There are two answers to this ... (1) Simple : MUAC is recognised as an independent criteria for defining acute malnutrition (wasting). So, ignoring measurement errors, the sensitivity of MUAC for detecting acute malnutrition is 100%. (2) Complicated : The answer above might have read better as "the sensitivity of MUAC for detecting malnutrition as defined by MUAC is 100%. The complication is that we can ALSO define acute malnutrition using a weight-for-height reference. Here the case definition is usually WHZ < -2 (for GAM) and WHZ < -3 (for SAM) using the WHO reference population. We now have (e.g.) SAM defined as MUAC < 115 mm OR WHZ < -3. This means that the sensitivity of using MUAC to detect cases defined by WHZ (and the sensitivity of using WHZ to detect cases defined by MUAC) depends on the degree to which these two sets of cases overlap. In young children the degree of overlap tends to be large. In some settings the degree of overlap is large for all children. In other settings the degree of overlap is small. This is particularly true in older children in pastoralist populations. In these populations the sensitivity of MUAC detecting WHZ cases and WHZ detecting MUAC cases may be quite low. There are many good reasons for preferring to use MUAC over WHZ. This has been the topic of several postings here. If you are wedded to using WHZ than you can still have some of the the advantages of MUAC (i.e. low cost, acceptability, rapidity, &c.) by using it in a two stage screen. In this you will screen using MUAC at a high threshold (e.g. 135 mm) and use WHZ only on those children with MUACs below this threshold. Here is an example for SAM: Screen using MUAC < 135 mm if MUAC < 115 mm then SAM else ... if MUAC between 115 and 134 mm (inclusive) then ... measure weight and height calculate WHZ if WHZ < -3 then SAM Since most children will have MUAC > = 135 mm and a few children will have MUAC < 115 mm this method means we only have to measure weight and height and calculate WHZ for a relatively small number of children. If you pick the threshold well and have well trained staff then you will have 100% detection of MUAC cases and WHZ cases in the children screened. WARNING : It is best to avoid using the two stage approach with (e.g.) children with MUAC < 135 mm being referred to centres for WHZ screening as this results in a lot of children being rejected by the program. This "problem of rejected referrals" has been shown to be a major cause of low coverage in CMAM programs and should be avoided. I hope this helps.

l would agree with Mark that MUAC measurements are accurate for screening severe malnutrition but it requires that the persons be trained to be able to also pick out bilateral oedema which is also a form of severe malnutrition

Yes. You will need to do this with WHZ and MUAC. It is most important when using WHZ as the retained water increased weight which will bias WHZ upwards. It is not such a problem when using MUAC as many children with oedema tend to also have low MUACs.