Effect of body shape on weight-for-height and MUAC in Ethiopia

Summary of research¹

Measuring a young child's MUAC

In November 2005, a survey undertaken in rural areas of Belete Weyne district of Somalia by Save the Children UK (SC UK) found that standard Weight for Height Z-scores (WHZ) and Mid Upper Arm Circumference (MUAC) based casedefinitions returned different estimates of the prevalence of acute malnutrition in pastoralist and agropastoralist livelihood zones. However, they produced similar estimates of the prevalence of global acute malnutrition in the riverine-agrarian livelihood zone. A small study undertaken to investigate this finding determined that children from the pastoralist and agro-pastoral livelihood zones tended to have longer limbs and lower sitting to standing height ratios than children from the riverine-agrarian livelihood zone.

In May 2006, the Emergency Nutrition Co-ordinating Unit of the Government of Ethiopia, funded by UNICEF with personnel and logistics support provided by SC UK and Concern Worldwide, initiated a study to investigate the relationship between WHZ and body-shape and the relationship between MUAC and body-shape in different populations.

Six cross-sectional nutritional anthropometry surveys were undertaken.The combined survey datasets formed the study sample. Data sources were grouped according to the livelihood zone from which data originated. Case definitions of acute malnutrition using WHZ calculated using both the NCHS and WHO reference populations and MUAC uncorrected for age or height were used. The sitting to standing height ratio was used as an index of body shape. The association between body shape and different case definitions of acute malnutrition were investigated using standard statistical techniques.

WHZ and MUAC case-definitions yielded similar estimates of the prevalence of acute malnutrition in agrarian children but different estimates of the prevalence of acute malnutrition in pastoralist children. These populations also exhibited different sitting to standing height ratios. Sitting to standing height ratio was an important predictor of weight-for-height. Sitting to standing height ratio was a poor predictor of MUAC.

The authors found that WHZ and WHZ casestatus in children are associated with body shape and may overestimate the prevalence of acute malnutrition in some populations. Their conclusion is that consideration should be given to whether WHZ should be replaced by MUAC for the purposes of estimating the prevalence of acute malnutrition.

For further information, contact Mark Myatt via website: www.brixtonhealth.com

¹Myatt. M et al. In press. The effect of body shape on weight-forheight and mid upper arm circumference based case-definitions of acute malnutrition in Ethiopian children. Accepted for publication in 'The Annals of Human Biology', due out in early 2009.