Purpose We aimed to describe the prevalence of undernutrition in hospitalised infants aged under 6 months and test the utility of simple index measures to detect undernutrition.

Design Diagnostic accuracy study: weight, length, mid-upper arm circumference (MUAC), triceps and subscapular skinfolds were measured in infants aged 2 weeks to 6 months admitted to a Teaching Hospital in Enugu, Nigeria. Index criteria: low (<−2SD) weight-for-age Z-scores (WAZ), weight-for-length Z-scores (WLZ); MUAC <11 cm. Reference definition: weight faltering (conditional weight gain below fifth percentile for healthy Nigerian infants) or sum of skinfolds (SSF) <10 mm.

Results Of 125 hospitalised infants, only 5% (6) were admitted specifically for undernutrition, but low SSF were found in 33% (41) and, 24% (25) with known birth weight had weight faltering, giving an undernutrition prevalence of 36%. Low WAZ was the most discriminating predictor of undernutrition (sensitivity 69%, positive predictive value 86%, likelihood ratio 5.5; area under receiver operator curves 0.90) followed by MUAC (73%, 73%, 4.9; 0.86), while WLZ performed least well (49%, 67%, 2.9; 0.84). Where both MUAC and WAZ were low, there was sensitivity 90%, positive predictive value 82% and likelihood ratio 8.7.

Conclusions Infants aged under 6 months admitted to hospital in Nigeria had a high prevalence of undernutrition. In young, high-risk population, a low WAZ alone was a valuable screening criterion, while combining weight with MUAC gave even higher discrimination. Measurement of length to calculate WLZ was a less useful predictor in this population.