160 Chapter 7 preterm infants. Hartnoll and colleagues, however, did show similar results as late nineteenth century cadaver studies, even though no comparative analysis was done.63 A conclusion thus cannot be drawn based on human studies in preterm infants, but is deemed reliable based on carcass analysis of piglets.37 Accuracy of DXA There are no comparative studies with preterm infants where DXA was compared with other methods, such as isotope dilution. DXA has been validated in piglets 38,40 and in practice is accepted as an accurate measure. Nevertheless, in human as well as animal studies DXA has been reported to overestimate fat mass, especially in lower weights. 40,64 Moreover, different software algorithms yield varying results in body composition.41 It would be insightful to investigate the agreement between isotope dilution, ADP and DXA in preterm infants. This would help to give us guidance on which method should be preferentially used to assess body composition in preterm infants. Patient-friendliness, ease of use and costs Methods are chosen based on local experience and available resources. In a clinical setting there is a preference for quick, easy-to-use, but accurate methods, which could be used at the bedside. In contrast, in a research setting there is more room for less flexible methods. Body proportionalitymeasures are quick, low-cost andminimally invasivemethods. They are ideal in the intensive care setting as well as in outpatient department for follow-up. Unfortunately, studies so far have not confirmed these methods have sufficient accuracy. Likewise, SFT and bioelectrical impedance techniques are easy bedside methods, but robust evidence supporting their use is lacking. Moreover, there is a high inter-observer variability and in extremely preterm infants SFT measurements should be taken with caution to prevent injury of their vulnerable skin. Nevertheless, when used with caution SFT is a safe, non-invasive method.10 DXA, ADP, and isotope dilution are accurate methods, but have some practical downsides. For DXA infants need to be clinically stable and free from respiratory support and monitoring, making DXA more appropriate from term age onwards. Taking into account that movement is not allowed, it could be used in infants up to 6 months corrected age who can be swaddled or nursed to sleep during the procedure. ADP could be used in the NICU if the infant is clinically stable and not on respiratory support. Nonetheless, the machinery is bulky and recalibration is needed after movement, making it less suitable for such use.
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