To the Editor: We appreciate the feedback provided by Drs Demerath and Fields (1) and the opportunity to respond to concerns they have raised with our publication. First, we studied 6–48 mo olds using the air-displacement plethysmography (ADP) device because infants in our longitudinal studies exceeded US Food and Drug Administration limit of the infant ADP device (18 kg) in the 4–6 mo range and we required a way of measuring body composition throughout early childhood for our longitudinal studies. The Food and Drug Administration Medical Device database lists the ADP device as approved for individuals 18 y and older (http://www.accessdata.fda.gov/cdrh_docs/pdf6/K060848.pdf), so special permission was obtained from our institutional review board to use the device in the age range of our study participants. Research from multiple independent laboratories is needed to determine whether the Pediatric Option for the BOD POD can fill the gap between the infant ADP device and that for adults.

The authors raise concerns about the effect of crying on measurement validity. In fact, to prevent child distress, very few children in our study were tested while crying. However, any loud vocalizations (such as singing or talking loudly to parents) were given a high vocalization score according to our protocol. Considering the high rates of distress (40%) during testing in the Fields study (2) and the frequency of our observations of loud vocalizations, we believe that a developmentally appropriate method for body fat testing will have to be robust enough to tolerate the variety of behaviors observed in young children in order to be useful in research and clinical settings. This same belief was put forward in the original validation paper for the infant ADP device (3), which specifically ensured that infant crying, urination, and defecation would not affect the accuracy of results, as these developmentally normative behaviors were unavoidable during test conditions.

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