title: Red blood cell (RBC) volume can be independently determined in vivo in humans using RBCs labeled at different densities of biotin.
abstract: BACKGROUND
  Anemia is a serious problem in critically ill neonates. To investigate the pathophysiology of anemia and responses to red blood cell (RBC) transfusions and erythropoietin therapy, repeated measurement of red blood cell volume (RCV) and blood volume is useful. To extend our previous sheep study in which RBCs were labeled at four different biotin densities, we assessed the validity of this multidensity method for in vivo measurement of circulating RCV in humans.
  
  
  METHODS
  In eight healthy adults, autologous RBCs were biotinylated at each of four biotin densities (6, 18, 54, and 162 µg biotinylation reagent/mL RBC), mixed, and infused intravenously; blood was sampled at 10, 20, and 60 minutes. At each time, RCV was calculated from dilution of individual RBC populations enumerated by flow cytometry. RCV measurements from the population of RBCs biotinylated at 6 µg/mL were chosen as the reference values because this density had been previously validated against the 51Cr method in vitro and in vivo in humans.
  
  
  RESULTS
  Values for RCVs were not significantly different among the four densities of biotinylated RBCs at any of the three time points and did not change over 60 minutes.
  
  
  CONCLUSIONS
  These studies provide evidence that four densities of biotinylated RBCs can be used in vivo for simultaneous, independent, accurate measurements of RCV in humans. We speculate that this method will also be useful for repeated measurement of RCV and blood volume in infants and other patient populations in whom radioactive labels should be avoided.
authors.affiliation: Department of Biochemistry & Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA. mockdonaldm@uams.edu
authors.forename: Donald M
authors.initials: DM
authors.lastname: Mock
authors.forename: Nell I
authors.initials: NI
authors.lastname: Matthews
authors.forename: Shan
authors.initials: S
authors.lastname: Zhu
authors.forename: Leon F
authors.initials: LF
authors.lastname: Burmeister
authors.forename: M Bridget
authors.initials: MB
authors.lastname: Zimmerman
authors.forename: Ronald G
authors.initials: RG
authors.lastname: Strauss
authors.forename: Robert L
authors.initials: RL
authors.lastname: Schmidt
authors.forename: Demet
authors.initials: D
authors.lastname: Nalbant
authors.forename: Gretchen A
authors.initials: GA
authors.lastname: Cress
authors.forename: John A
authors.initials: JA
authors.lastname: Widness
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001710:Biotin / Q000378:metabolism*; D004911:Erythrocyte Volume; D004912:Erythrocytes / Q000166:cytology* / Q000378:metabolism*; D006801:Humans; D008875:Middle Aged; D055815:Young Adult
chemical_list: D001710:Biotin