title: The diagnostic accuracy of multi-frequency bioelectrical impedance analysis in diagnosing dehydration after stroke.
abstract: BACKGROUND
  Non-invasive methods for detecting water-loss dehydration following acute stroke would be clinically useful. We evaluated the diagnostic accuracy of multi-frequency bioelectrical impedance analysis (MF-BIA) against reference standards serum osmolality and osmolarity.
  
  
  METHODS
  Patients admitted to an acute stroke unit were recruited. Blood samples for electrolytes and osmolality were taken within 20 minutes of MF-BIA. Total body water (TBW%), intracellular (ICW%) and extracellular water (ECW%), as percentages of total body weight, were calculated by MF-BIA equipment and from impedance measures using published equations for older people. These were compared to hydration status (based on serum osmolality and calculated osmolarity). The most promising Receiver Operating Characteristics curves were plotted.
  
  
  RESULTS
  27 stroke patients were recruited (mean age 71.3, SD10.7). Only a TBW% cut-off at 46% was consistent with current dehydration (serum osmolality >300 mOsm/kg) and TBW% at 47% impending dehydration (calculated osmolarity ≥295-300 mOsm/L) with sensitivity and specificity both >60%. Even here diagnostic accuracy of MF-BIA was poor, a third of those with dehydration were wrongly classified as hydrated and a third classified as dehydrated were well hydrated. Secondary analyses assessing diagnostic accuracy of TBW% for men and women separately, and using TBW as a percentage of lean body mass showed some promise, but did not provide diagnostically accurate measures across the population.
  
  
  CONCLUSIONS
  MF-BIA appears ineffective at diagnosing water-loss dehydration after stroke and cannot be recommended as a test for dehydration, but separating assessment by sex, and using TBW as a percentage of lean body weight may warrant further investigation.
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich, UK. m.kafri@uea.ac.uk
authors.forename: Mohannad W
authors.initials: MW
authors.lastname: Kafri
authors.forename: Phyo Kway
authors.initials: PK
authors.lastname: Myint
authors.forename: Danielle
authors.initials: D
authors.lastname: Doherty
authors.forename: Alexander Hugh
authors.initials: AH
authors.lastname: Wilson
authors.forename: John F
authors.initials: JF
authors.lastname: Potter
authors.forename: Lee
authors.initials: L
authors.lastname: Hooper
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001825:Body Fluid Compartments / Q000378:metabolism; D001834:Body Water; D003681:Dehydration / Q000097:blood / Q000175:diagnosis* / Q000209:etiology*; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration; D012372:ROC Curve; D020521:Stroke / Q000097:blood / Q000150:complications*