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Mid-Upper Arm Circumference (MUAC)


Theoretical problems with MUAC
Practical problems with MUAC
Summary - the use of MUAC

MUAC is the circumference of the left upper arm, measured at the mid-point between the tip of the shoulder and the tip of the elbow (olecranon process and the acromium). In children, MUAC is useful for the assessment of nutritional status 51, 52, 53, 54, 55 56. It is good at predicting mortality and in some studies, MUAC alone 57, 58, 59 or MUAC for age 10, predicted death in children better than any other anthropometric indicator. This advantage of MUAC was greatest when the period of follow-up was short 60.

The MUAC measurement requires little equipment and is easy to perform even on the most debilitated individuals. Although it is important to give workers training in how to take the measurement in order to reduce inter- and intra- observer error, the technique can be readily taught to minimally trained health workers 61. It is thus potentially suited to screening admissions to feeding centres during emergencies. The use of MUAC in emergencies is, however, still controversial, and disagreement over the preferential selection of younger children, the levels of cut-off points used, the efficiency of a two-phase screening process and poor reproducibility in the measurement continue 62, 63, 64, 65, 66. Consequently, some humanitarian relief agencies remain sceptical about the use of MUAC in emergencies 67.

At present during emergencies, MUAC is only recommended for use with children between one and five years of age 68, 37, 38. It is, however, increasingly being used to assess adult undernutrition during famine 69, 70, 71. Measurements of adult MUAC have long been known to reflect changes in adult body weight 72, and the major determinants of MUAC, arm muscle and sub-cutaneous fat, are both important determinants of survival in starvation 73, 74, 42. As MUAC is less affected than BMI by the localised accumulation of excess fluid (pedal oedema, periorbital oedema, ascites) common in famine, it is likely to prove to be a more sensitive index of tissue atrophy than low body weight. It is also relatively independent of height 70.

The use of MUAC has not been evaluated as a prognostic indicator. However, estimates of arm muscle area (AMA) or corrected arm muscle area (CAMA), corrected for humerus cross-sectional area, have been incorporated into diagnostic schemes for adult undernutrition in hospitals 75 and used as prognostic indicators in the elderly and in cancer patients 76, 77. However, it is unlikely that CAMA or AMA will be of use in emergency assessments as both require accurate measures of skin-fold thickness that would be hard to obtain given the rush and pressure of an emergency operation.

Ferro-Luzzi and James 36 have proposed MUAC cut-off points for use in screening acute adult undernutrition. They base these on extrapolation from more normally nourished populations in developing countries, without reference to data from acutely undernourished adults during famine. Although there is some evidence that the undernourished category may be associated with increased morbidity in chronically undernourished populations19, we doubt whether the criteria proposed are appropriate for screening acutely undernourished adults.

Data from famines suggest that the relationship between MUAC and BMI is not constant during acute undernutrition and that an accelerated loss of peripheral tissue during acute undernutrition has a relatively greater depressing effect on MUAC than upon BMI 71. These data also suggest that during acute undernutrition the differences in MUAC between men and women become less pronounced, a finding supported by previous observations in more normally nourished population 78.

It is likely, therefore, that in populations suffering from famine, MUAC cut-off points denoting moderate to severe undernutrition should be adjusted. Values of 185 mm denoting moderate undernutrition and 160 mm denoting severe undernutrition in both sexes have been proposed and used in famines 71. Given that there are different cross-sectional humerus bone areas in men versus women 79, it is unclear whether common cut-off points for both sexes will prove appropriate.

Theoretical problems with MUAC

Lack of data upon which to decide useful cutoff points - There are insufficient data available correlating MUAC with mortality and other functional measures in adults. Cut-off points based on risk of mortality cannot, therefore, be presented with any degree of certainty. There exists a need for more field studies during emergency famine-relief operations to evaluate the power of MUAC to predict adult mortality in different famine affected populations.

Age - The use of MUAC in adults may be affected by the redistribution of subcutaneous fat towards central areas of the body during ageing 80, 19. In older children and adolescents, the rapidly changing patterns of skeletal muscle and subcutaneous fat are also likely to be a problem. Age specific MUAC cut-off points may be required for older children, adolescents, and the elderly.

Ethnicity - Ethnic differences in MUAC have not been sufficiently studied to determine whether a single cut-off point for MUAC could be used for all ethnic groups.

Practical problems with MUAC

Measurement error - In children, the use of MUAC is associated with two problems: the preferential selection of younger children as undernourished 66, 81, 9 and a lack of reproducibility in MUAC measurements 65. Problems with the reproducibility of MUAC measurements are potentially a more serious obstacle to the use of MUAC in adults. As in children, both inter- and intra- observer errors in MUAC measurements may occur. The importance of these errors needs to be investigated, but it is likely that the larger dimension of the adult arm will reduce the relative importance of such errors. The development of colour-banded numeric MUAC bands reflecting threshold values of MUAC with a change of colour would further reduce these problems by removing numerical errors. Given the ease with which MUAC measurements can be performed it would be feasible to refer any patients found to have a MUAC within a few millimetres on either side of the threshold (designated on the band as a different coloured zone) to a more experienced worker for verification or for further (e.g. clinical) assessment as part of a two-stage screening process. The width of this zone should be based upon a more detailed examination of errors in the evaluation of adult MUAC by minimally trained workers. Colour-banded MUAC measurement straps are already in use with children.

The assessment of adult nutritional status using MUAC requires no equipment apart from a tape measure. As the index is the actual measurement itself, mathematical manipulation of the measurement obtained is not necessary. The ease with which MUAC can be assessed make it suitable for nutritional screening during the height of an emergency where time and skilled personnel are at a premium.

Summary - the use of MUAC

In our opinion, MUAC is an appropriate indicator for the assessment of acute adult undernutrition. The indicator is useful for both screening acute adult undernutrition and for estimating prevalence of undernutrition at a population level. We suggest, that until more data are available, the following cutoff points are used for both sexes for screening adult admissions to feeding centres:"

Table 3 Suggested MUAC cut-off points for moderate and severe acute adult undernutrition

Level of undernutrition

MUAC (mm)

Moderate

< 185

Severe

< 160


At present there is insufficient data to assess the usefulness of MUAC as a tool with which to monitor treatment in adult feeding centres. More data is required to assess this role.


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