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Poor nutritional status adversely affects long term survival of patients with cystic fibrosis (CF).1 Body composition measured by dual energy x ray absorptiometry (DXA) has been shown to correlate well with other established techniques such as bioelectric impedance analysis and total body potassium estimation.2 This study was designed to compare the whole body and regional bone mineral density of children with CF with that of controls, the results of which have been reported previously.3 Here, we present the results of post hoc comparison of DXA measured whole body lean body mass (LBM) in 28 patients with CF (aged 5–16 years) and 49 healthy gender, age, height, weight, and pubertal stage matched controls. Hologic QDR 4500 Acclaim DXA scanner (Hologic Inc., Waltham, MA, USA) in conjunction with the V8.24a:3 software was used for whole body LBM measurements. The short term in vivo precision for total body LBM in adults is 1.75%. Disease severity in cystic fibrosis patients was estimated by the Shwachman Kulczycki (SK) score. The study design, recruitment of subjects, and anthropometric measurements has been described previously.3
We have previously shown that age, height, weight, body mass index, LBM, and fat body mass of subjects in the CF and control groups were not different.3 However, as shown in fig 1, the difference in LBM between CF patients and controls (LBM of CF patients minus LBM of age and gender matched controls) declined with age (slope −0.33; 95% CI −0.62 to −0.04; p = 0.028). In other words, the older CF patients had lower LBM in comparison to healthy age and size matched controls. An inverse relation was observed between SK scores and age in CF subjects (r = −0.39, p < 0.05), indicating that older CF patients had more severe disease compared to the younger patients. Taken together, these data suggest that in CF patients the disease severity worsens with age, and this in turn is associated with the decline in LBM. Alternatively, the observed reduction in LBM and lower SK scores in older patients might be due to a cohort effect, as the eldest patients were born almost 10 years earlier than the youngest patient, during which period significant advancements have occurred in the care of CF patients. Our data are potentially important, as poor nutritional status is known to adversely affect survival of CF patients,1 and changes in body composition are known to predate deterioration in traditional anthropometric indices of nutrition.4 A prospective longitudinal study is required to confirm our finding that LBM declines with age and/or worsening disease severity, and to evaluate its impact on morbidity and long term survival in CF patients.