title: Pitfalls in the assessment of body composition in survivors of acute lymphoblastic leukaemia.
abstract: BACKGROUND
  Body fat mass (FM) and fat free mass (FFM) in childhood are often estimated by conversion of a measured variable into compartmental body composition using constants or regression equations that have been previously derived in healthy individuals. Application of such constants or equations to children with disease states may lead to inappropriate conclusions since the "normal" relationships may become altered.
  
  
  OBJECTIVE
  To test this hypothesis by taking measurements of body composition using dual energy x ray absorptiometry (DEXA) as a "gold standard" method and calculating hydration and body potassium constants using isotopic water dilution and whole body potassium counting. Measurements of bioelectrical impedance (BIA) by two different analysers (RJL and Holtain) were also performed to allow comparison with body water measurements.
  
  
  RESULTS
  Measurements were performed in 35 children treated for acute lymphoblastic leukaemia (ALL) and compared to those in 21 children treated for a variety of other malignancies and 32 healthy sibling controls. The mean hydration and potassium content of FFM was significantly reduced in the ALL group compared to both other malignancies and controls. Application of equations derived from controls for the measurement of FFM derived from bioelectrical impedance led to an underestimation of 1.15 kg when compared to that derived from DEXA in children treated for ALL but not in other malignancies. For all groups combined, BIA was significantly different in the two analysers.
  
  
  CONCLUSIONS
  Care needs to be taken in the application of equations derived from the normal population to body composition measurement in children treated for ALL.
authors.affiliation: Department of Paediatrics, John Radcliffe Hospital, Oxford, UK. justin.warner@orh.nhs.uk
authors.forename: J T
authors.initials: JT
authors.lastname: Warner
authors.forename: W D
authors.initials: WD
authors.lastname: Evans
authors.forename: D K H
authors.initials: DK
authors.lastname: Webb
authors.forename: J W
authors.initials: JW
authors.lastname: Gregory
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000737:chemistry; D001823:Body Composition; D015992:Body Mass Index; D001834:Body Water / Q000737:chemistry; D002648:Child; D015331:Cohort Studies; D017097:Electric Impedance; D006801:Humans; D011188:Potassium / Q000032:analysis; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000503:physiopathology*; D017741:Survivors
chemical_list: D011188:Potassium