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Diagnostic measures for severe acute malnutrition in Indian infants under 6 months of age: a secondary data analysis
Ranadip Chowdhury1, Nitika2, Tarun Shankar Choudhary2
1Knowledge Integration and Translational Platform (KnIT) at Centre for Health Research and Development, Society for Applied Studies, 45, Kalu Sarai, New Delhi, 110016, India. ranadip.chowdhury@sas.org.in.
Insights
Weight for age z-score (WAZ) < -3 at 6 weeks is a better predictor of infant mortality than weight for length z-score (WLZ) or length for age z-score (LAZ). This finding suggests WAZ should be considered for diagnosing severe acute malnutrition (SAM) in infants under 6 months.
Area of Science:
- Pediatric Nutrition
- Infant Health
- Malnutrition Assessment
Background:
- Current definition of severe acute malnutrition (SAM) using weight for length z-score (WLZ) < -3 has limitations for infants under 6 months.
- WLZ and length for age z-score (LAZ) are less reliable for detecting undernutrition in infants under 6 months.
Purpose of the Study:
- To compare the predictive accuracy of WLZ, WAZ, and LAZ for infant mortality.
- To evaluate anthropometric indicators for diagnosing SAM in infants aged 6 weeks to 6 months.
Main Methods:
- Analysis of data from a randomized trial in Delhi, India.
- Infants' weight and length measured at 6 weeks; vital status tracked to 6 months.
- Calculated sensitivity, specificity, predictive values, and likelihood ratios for WAZ < -3, WLZ < -3, and LAZ < -3.
Main Results:
- WAZ < -3 demonstrated higher sensitivity (64.6%) compared to LAZ (39.1%) and WLZ (25.0%).
- WAZ < -3 showed a higher area under the receiver operating characteristic curve (0.75), indicating better discrimination of mortality.
- WAZ < -3 was associated with the highest adjusted relative risk (10.6) and population attributable fraction (57.9%) of mortality.
Conclusions:
- Weight for age z-score (WAZ) < -3 at 6 weeks is a superior predictor of death between 6 weeks and 6 months compared to WLZ < -3 and LAZ < -3.
- WAZ < -3 should be considered as a diagnostic criterion for SAM in infants under 6 months.
Background:
Weight for length z-score (WLZ) < - 3 is currently used to define severe acute malnutrition (SAM) among infants. However, this approach has important limitations for infants younger than 6 months of age as WLZ cannot be calculated using WHO growth standards if infant length is < 45 cm. Moreover, length for age z-score (LAZ) and weight for length z-score (WLZ) are least reliable measures, with high chances of variation, and less chances of detecting undernutrition in under 6 months infants. The objective of the current analysis was to compare WLZ with WAZ and LAZ in a cohort of Indian infants in predicting the deaths between 6 weeks and 6 months of age.
Methods:
The data was from an individually randomized trial conducted in slums of Delhi, India in which infants' weight and length were measured at 6 weeks of age (at the time of the first immunization visit). Vital status of the infants was documented from 6 weeks to 6 months of age. The sensitivity, specificity, positive and negative predictive values, and positive and negative likelihood ratios were calculated for WAZ < -3, WLZ < -3, and LAZ < -3 for deaths between 6 weeks and 6 months of age. The receiver operating characteristics curve was calculated for each of the above anthropometric indicators.
Results:
For deaths occurring between 6 weeks to 6 months of age, the specificity ranged between 85.9-95.9% for all three anthropometric indicators. However, the sensitivity was considerably higher for WAZ; it was 64.6% for WAZ < -3, 39.1% for LAZ < -3, and 25.0% for WLZ < -3. WAZ < -3 had higher area under curve (0.75; 95% CI: 0.68, 0.82) and hence, better discriminated deaths between 6 weeks and 6 months of age than WLZ < -3. The adjusted relative risk (RR 10.6, 95% CI 5.9, 18.9) and the population attributable fraction (PAF 57.9, 95% CI 38.8, 71.0%) of mortality was highest for WAZ < -3.
Conclusions:
We found WAZ < -3 at 6 weeks of age to be a better predictor of death in the 6 weeks to 6 months of life in comparison to WLZ < -3 and LAZ < -3 and propose that it should be considered to diagnose SAM in this age group.
