Classification of malnutrition in cystic fibrosis: implications for evaluating and benchmarking clinical practice performance.

BACKGROUND In 2005, the Cystic Fibrosis Foundation (CFF) revised the nutrition classification guidelines to eliminate the use of percentage of ideal body weight (%IBW) to define "nutritional failure"; the CFF also recommended that children with cystic fibrosis maintain a body mass index percentile (BMIp) > or = 50th. OBJECTIVE We assessed the effect of the 2005 CFF nutrition classification guidelines on evaluating the performance of nutritional care practices. DESIGN Data from 14,702 children reported to the 2002 CFF Patient Registry were analyzed to compare malnutrition rates in 113 cystic fibrosis centers in the United States. Nutritional failure was defined according to the 2002 CFF criteria--ie, height < 5th percentile, %IBW < 90%, or BMIp < 10th. "Below BMI goal" was defined according to the 2005 CFF criterion, ie BMIp < 50th. RESULTS Eliminating %IBW resulted in a 6% reduction (from 33% to 27%) in the nutritional failure rate in the United States. The use of BMIp < 50th led to the classification of 57% of children as below the BMI goal. Misclassification of nutritional failure according to %IBW ranged from 1% to 16% among 113 centers and was greater in the centers with a larger proportion of tall patients. After the elimination of %IBW, one-third of centers changed to a different tertile ranking for nutritional failure rates (kappa = 0.50, moderate-to-poor agreement). More than half the centers changed to a different tertile ranking, from nutritional failure to below BMI goal (kappa = 0.22, poor agreement). CONCLUSION Eliminating misclassification by %IBW and implementing the new BMI goal led to profound and unequal changes in malnutrition rates across cystic fibrosis centers.