Academic journal article Bulletin of the World Health Organization

The Development of MUAC-for-Age Reference Data Recommended by a WHO Expert Committee

Academic journal article Bulletin of the World Health Organization

The Development of MUAC-for-Age Reference Data Recommended by a WHO Expert Committee

Article excerpt

Introduction

For many years, mid-upper-arm circumference (MUAC) has been used as an alternative indicator of nutritional status if the collection of height and weight measurements was difficult, such as during emergencies, famines, or refugee crises. In such cases, low MUAC? determined on the basis of a single cut-off value, has been used as a proxy for low weight-for-height (i.e. wasting). Comparisons of the two indicators, however, show that they are poorly correlated (1, 2). Moreover, in community-based studies, MUAC appears to be a better predictor of childhood mortality than height- and weight-based anthropometric indicators (3-6). This has led to the proposal that MUAC should be used as an independent indicator for routine nutritional assessment.

The operational advantages of MUAC include the portability of measuring tapes and the fact that a single cut-off value (generally 12.5 cm or 13.0 cm) has been used for children [is less than] 5 years of age. The use of a fixed cut-off value was based on the observation in the early 1960s that for normal, well-fed Polish children MUAC increased by only about 1 cm between the ages of 1 year and 4 years, and that there was a difference of only a few millimetres between boys and girls at most ages (7, 8). However, the assumption that MUAC is age- and sex-independent in young children has recently been questioned, and it has been suggested that MUAC Z-scores that adjust for differences between age and sex are a more useful indicator of nutritional status (9, 10).

In 1993, a WHO Expert Committee reviewed the scientific evidence underlying the use and interpretation of MUAC (11). The Committee examined mean MUAC data across ages from the National Center for Health Statistics (NCHS) sample of children in the USA, and for a cohort of Malawian children; for both populations MUAC increased by approximately 2 cm between 6 and 59 months of age. When a MUAC-for-age reference for both boys and girls was constructed from the NCHS data and applied to the Malawian children, important differences were observed between the age-specific prevalences of low MUAC when either MUAC-for-age Z-scores or a cut-off value of 13.0cm were used (11). A fixed cut-off value preferentially identified younger children as malnourished.

The Committee concluded that the assumption of age independence did not reflect the true pattern of mid-upper-arm growth and recommended that proper interpretation of MUAC required the use of age-specific reference data (12). In this article, we explain the methodology for the development of these data, present age- and sex-specific growth curves and tables and discuss the applications and limitations of MUAC as a nutritional indicator.

Methods

To construct the MUAC-for-age growth reference data, we used growth data for children 6-59 months of age from the first and second National Health and Nutrition Examination Surveys in the USA (NHANES I, NHANES II). Both NHANES I and NHANES II used a complex, multistage, probability-sampling design to obtain a representative sample of the non-institutionalized civilian population aged 6 months to 74 years in the USA. Detailed descriptions of the samples have been published previously (13, 14). Data from both surveys were combined in order to increase sample size. A total of 2310 measurements of MUAC for NHANES I and 3309 measurements for NHANES II were available for children aged 6-59 months. We verified that age-and sex-specific growth status were comparable in both surveys.

We estimated the mean and standard deviation (SD) of MUAC for each month of age by combining MUAC data for the relevant month of age with data for the 3 months before and 3 months after the age concerned.(a) A linear regression of the resulting 7-month segment of MUAC data by age provides a more stable estimate of the mean and SD of MUAC at the mid-point month than that based on the data for that month only. …

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