Validation, optimal threshold determination, and clinical utility of the Infant Risk of Overweight Checklist (IROC) for early prevention of child overweight

Background: Previous research has demonstrated the predictive validity of the Infant Risk of Overweight Checklist (IROC). This study further establishes the predictive accuracy of the IROC using data from the Avon Longitudinal Study of Parents and Children (ALSPAC) and examines the optimal threshold for determining high risk of childhood overweight. Methods: Using the IROC algorithm, we calculated the risk of being overweight, based on International Obesity Task Force (IOTF) criteria, in the first year of life for 980 children in the ALSPAC cohort at 5 years. Discrimination was assessed by the area under the receiver operating curve (AUC c¬¬-statistic). Net reclassification index (NRI) was calculated for risk thresholds ranging from 2.5% to 30% which determine cut-offs for identifying infants at risk of becoming overweight. Results: At five years of age, 12.3% of boys and 19.6% of girls were categorised overweight. Discrimination (AUC c-statistic) ranged from 0.67 (95% CI 0.62 – 0.72) when risk scores were calculated directly to 0.93 (95% CI 0.88 – 0.98) when the algorithm was recalibrated and missing values of the risk factor algorithm were imputed. The NRI showed there were positive gains in reclassification using risk thresholds from 5% to 20%, with the maximum NRI being at 10%. Conclusions: This study confirms the IROC has moderately good validity for assessing overweight risk in infants and offers an optimal threshold for determining high risk. The IROC algorithm has been imbedded into a computer programme for Proactive Assessment of Obesity Risk during Infancy (ProAsk) which facilitates early overweight prevention through communication of risk to parents. http://online.liebertpub.com/doi/full/10.1089/chi.2015.0246