title: Bioelectrical impedance measurements in patients with gastrointestinal disease: validation of the spectrum approach and a comparison of different methods for screening for nutritional depletion.
abstract: BACKGROUND
  Bioelectrical impedance spectroscopy (BIS) may be of value in identifying patients with nutritional depletion.
  
  
  OBJECTIVE
  The primary aim of the study was to assess the validity of BIS in patients with gastrointestinal disease. The secondary aim was to compare different screening methods for identifying nutritionally depleted patients.
  
  
  METHODS
  In 70 patients with gastrointestinal disease, BIS measurements were performed and fluid compartments were calculated from extrapolated resistance (R) values of extracellular (R(ECW)) and intracellular (R(ICW)) water based on mixture equations. Results were compared with total body water and ECW, which were measured by dilution methods. Patients were classified as depleted if their actual fat-free mass (FFM) was <90% of their ideal FFM (iFFM). Different screening approaches for depletion were compared: the impedance vector method and the resistance index (RI) in relation to iFFM (RI/iFFM).
  
  
  RESULTS
  Total body water and ICW were largely underestimated (4 L) in the not-depleted patients but not in the depleted patients. In both groups, ECW was slightly overestimated (0.6-0.7 L). The critical frequency was 60% higher and the membrane capacitance was 40% lower in the depleted than in the not-depleted patients. The impedance vector method failed to identify depleted patients, whereas the proposed ratio at R(50) (R measured at 50 kHz) and R(inf) (R at infinite frequency) resulted in comparable sensitivity (86%) and specificity (73-80%).
  
  
  CONCLUSIONS
  BIS measures of body fluids are influenced by the presence of depletion, probably because of alterations in the electric properties of the body at the cellular level. However, for screening purposes, the use of the ratio (L(2)/R)/iFFM at R(50) and R(inf) may be of value.
authors.affiliation: Department of Dietetics, University Hospital Maastricht, P Debyelaan 25, PO Box 5800, 6202 AZ Maastricht, Netherlands. ncox@pmdi.azm.nl
authors.forename: Petronella L M
authors.initials: PL
authors.lastname: Cox-Reijven
authors.forename: Bernard
authors.initials: B
authors.lastname: van Kreel
authors.forename: Peter B
authors.initials: PB
authors.lastname: Soeters
mesh_terms: D000368:Aged; D001823:Body Composition; D015992:Body Mass Index; D001834:Body Water / Q000378:metabolism; D017097:Electric Impedance; D005110:Extracellular Space; D005260:Female; D005767:Gastrointestinal Diseases / Q000503:physiopathology*; D006801:Humans; D007201:Indicator Dilution Techniques; D042541:Intracellular Space; D008297:Male; D044342:Malnutrition / Q000175:diagnosis* / Q000209:etiology; D008875:Middle Aged; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity