Comparison of WHO and CDC Growth Charts in Predicting Pulmonary Outcomes in Cystic Fibrosis

Objectives: The relation of weight-for-length (WFL) and weight-for-age (WFA) measurements with pulmonary function in patients with cystic fibrosis (CF) using the World Health Organization (WHO) growth standards has not been evaluated. The objective of the present study was to show that the relation of WFL and WFA measurements at 2 years with forced expiratory volume in 1 second (FEV1) at 6 to 8 years differs when using the WHO versus the Centers for Disease Control and Prevention (CDC) growth charts. Methods: We assessed 1155 patients in the CF Foundation Patient Registry born between 2001 and 2004. Comparisons were made between the CDC and WHO growth charts. Results: The WFL percentiles are significantly higher for the WHO growth standards compared with those for the CDC growth charts (median and interquartile range [IQR] WHO-64.8 [41.7-84.9], CDC-48.1 [23.7-75.7], P<0.0001). WFL and WFA percentiles at 2 years on both charts are strongly associated with FEV1 at 6 to 8 years of age. The FEV1 at 6 to 8 years was statistically significantly lower for children who were classified as reaching a WFL >= 50th percentile at 2 years by WHO standards alone versus those who qualified by both growth charts (median and IQR 103 [94-115] vs 107 [96-117], P<0.05). Continued weight gain between 2 and 6 years was associated with a higher lung function at age 6 to 8 years. Conclusions: Although children attaining the 50th WFL percentile on the WHO growth chart by age 2 years have a lower FEV1 at 6 years than children attaining the same percentile on the CDC chart, both groups of children attain clinically normal FEV1. Further studies are needed to determine whether this difference is clinically meaningful.