ARE BIOELECTRIC IMPEDANCE MEASUREMENTS VALID IN PATIENTS WITH CYSTIC-FIBROSIS

This pilot study compared the use of bioelectric impedance analysis (B IA), a rapid, portable, and painless method of measuring body composit ion, to isotope dilution in patients with and without cystic fibrosis (CF). Many methods exist for measuring body composition but these meas ures can be difficult to use in the clinical setting. BIA has been val idated as a tool for nutritional assessment in healthy adults, but it must be validated in patient populations with specific disease-related nutritional problems, such as CF. Ten ambulatory patients with CF wer e selected along with ten controls matched for age, sex, and body mass index (BMI; wt/ht2). Total body water (TBW) was determined using isot ope-ratio mass spectrometry on urine specimens before and after patien ts consumed 0.2 g/kg deuterium-rich water. BIA was performed using a t etrapolar technique; 500 muA of current at 50 kHz was introduced and t he voltage drop measured. Seven men and three women were studied in ea ch group. Median age was 27 (range, 18-39) and median BMI was 19.2 (ra nge, 16.7-30.1) in CF adults. Median age was 27.5 (range, 15-43) and m edian BMI was 20.7 (range, 19.4-31.6) in controls. The resistance inde x (RI; ht2/resistance) correlated strongly with TBW in patients with C F (r = 0.88; y = 0.482x + 11.138; p < 0.05) as well as in controls (r = 0.87; y = 0.661x + 1.299; p < 0.05). We conclude that BIA is a rapid , portable, and painless method for measuring body composition that co rrelates well with the deuterium-dilution method. However, CF-specific regression equations will need to be developed and confidence interva ls defined using large numbers of patients before this technique can b e widely applied to patients with CF.